A functional carbon source, a preparation method and application thereof, and a carbon-coated lithium iron phosphate main material and a preparation method thereof

Abstract

The present application relates to the technical field of lithium ion battery cathode material, in particular to a functional carbon source, a preparation method and application thereof, and a carbon-coated lithium iron phosphate main material and a preparation method thereof.The functional carbon source is polymerized from two or more of an acrylic monomer, an ammonium monomer, a phosphoric acid monomer, an aromatic hydrocarbon monomer and a nitrogen-containing heterocyclic monomer; the number average molecular weight of the functional carbon source is 5000-50000 Da.The functional carbon source is designed by multi-gradient copolymerization of the acrylic monomer, the ammonium monomer, the phosphoric acid monomer, the aromatic hydrocarbon monomer and the nitrogen-containing heterocyclic monomer, combined with the mode of monomer molar ratio regulation and main chain-branched molecular structure directional construction, to realize the improvement of the sanding solid content of the lithium iron phosphate precursor slurry and the shortening of the sanding time, and simultaneously realize the effects of high residual carbon rate of the carbon source and uniform and dense carbon coating layer, finally significantly enhance the gram capacity and rate performance of the lithium iron phosphate, and the carbon source preparation process is simple, suitable for the existing industrial production process, and easy to popularize and apply.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery cathode material technology, specifically to a functional carbon source and its preparation method and application, and a carbon-coated lithium iron phosphate main material and its preparation method. Background Technology

[0002] Lithium iron phosphate (LiFePO4, LFP) is widely used in electric vehicles, energy storage devices, and other fields due to its low cost, environmental friendliness, long cycle life, and excellent safety. However, lithium iron phosphate itself has poor electronic and ionic conductivity, requiring carbon coating modification to improve its conductivity. Furthermore, the solid content and milling efficiency of the lithium iron phosphate precursor slurry directly affect production efficiency and product consistency. Existing carbon sources struggle to achieve a synergistic improvement in both slurry processing performance and the electrochemical performance of lithium iron phosphate.

[0003] Currently used carbon sources include sugars such as glucose, sucrose, and starch, as well as conductive carbon powders such as acetylene black and graphite. Sugar-based carbon sources have low residual carbon rates and uneven carbon coatings, and they cannot effectively increase solids content during slurry milling, easily leading to high slurry viscosity and excessively long milling times. While conductive carbon powders can improve conductivity, they have poor dispersibility and are prone to agglomeration, affecting carbon coating effectiveness and slurry stability. Some modified carbon sources have attempted binary or ternary monomer combinations, but these suffer from limited functionality and cannot simultaneously achieve the multiple objectives of optimized milling performance, high residual carbon rates, uniform carbon coating, and improved electrochemical performance.

[0004] Therefore, developing a functional carbon source that combines high dispersibility, high residual carbon rate, and excellent carbon coating ability to simultaneously improve the sand milling performance of lithium iron phosphate precursor slurry and the electrochemical performance of lithium iron phosphate has become a technical problem that the industry urgently needs to solve. Summary of the Invention

[0005] To address the shortcomings of existing technologies for lithium iron phosphate carbon sources, which struggle to balance slurry processing performance and electrochemical performance, and which suffer from low residual carbon content, uneven coating, and low slurry solids content during sand milling, as well as poor dispersion and easy agglomeration of conductive carbon powder, and the limited functionality of modified carbon sources that fail to achieve multiple objectives such as optimized sand milling performance, high residual carbon content, uniform carbon coating, and improved electrochemical performance, this invention provides a functional carbon source. This functional carbon source utilizes a multi-component gradient copolymerization design of acrylic monomers, ammonium monomers, phosphate monomers, aromatic monomers, and nitrogen-containing heterocyclic monomers. By combining monomer molar ratio control with directional construction of main-chain and branch-chain molecular structures, it achieves increased solids content and shortened sand milling time in lithium iron phosphate precursor slurry. Simultaneously, it achieves high residual carbon content and a uniform and dense carbon coating layer, ultimately significantly enhancing the specific capacity and rate performance of lithium iron phosphate. Furthermore, this carbon source has a simple preparation process, is compatible with existing industrial production processes, and is easy to promote and apply.

[0006] To achieve the above objectives, in a first aspect, the present invention provides a functional carbon source, which is polymerized from two or more of acrylic monomers, ammonium monomers, phosphate monomers, aromatic monomers and nitrogen-containing heterocyclic monomers; The number-average molecular weight of the functional carbon source is 5000~50000 Da.

[0007] Preferably, the acrylic monomer is selected from one or more of acrylic acid, methacrylic acid, and ethyl acrylate.

[0008] Preferably, the ammonium monomer is selected from one or more of ammonium acrylate, methacrylamide, and dimethyl diallyl ammonium chloride.

[0009] Preferably, the phosphate monomer is selected from one or more of vinyl dihydrogen phosphate, propylene dihydrogen phosphate, and vinylphosphonic acid.

[0010] Preferably, the aromatic monomer is selected from one or more of styrene, p-methylstyrene, and vinylnaphthalene.

[0011] Preferably, the nitrogen-containing heterocyclic monomer is selected from one or more of pyrrole, pyridine, and imidazole.

[0012] Preferably, in the functional carbon source, by molar percentage, acrylic monomers account for 20-45%, ammonium monomers account for 0-20%, phosphate monomers account for 0-18%, aromatic monomers account for 0-60%, and nitrogen-containing heterocyclic monomers account for 0-50%; the sum of the molar percentages of each monomer is 100%.

[0013] Preferably, in the functional carbon source, acrylic monomers serve as the main chain backbone and / or branched functional groups; ammonium monomers are embedded in the main chain or serve as branched monomers; phosphate monomers are grafted onto the main chain or form copolymer branches; aromatic monomers form copolymer branches or are embedded in the main chain; and nitrogen-containing heterocyclic monomers serve as branched functional monomers.

[0014] Secondly, the present invention provides a method for preparing a functional carbon source as described in the present invention, the method comprising the following steps: 1) Dissolve water-soluble monomers in water to obtain an aqueous solution; dissolve oil-soluble monomers in an organic solvent to obtain an organic solution; 2) First, heat the aqueous solution, then add dropwise a mixture of organic solution and initiator to carry out the polymerization reaction, cool, adjust the pH, evaporate and concentrate, and dry to obtain a functional carbon source; The water-soluble monomer is selected from one or more of acrylic monomers, ammonium monomers, and phosphate monomers; The oil-soluble monomers are aromatic monomers and / or nitrogen-containing heterocyclic monomers.

[0015] Preferably, the acrylic monomer is selected from one or more of acrylic acid, methacrylic acid, and ethyl acrylate.

[0016] Preferably, the ammonium monomer is selected from one or more of ammonium acrylate, methacrylamide, and dimethyl diallyl ammonium chloride.

[0017] Preferably, the phosphate monomer is selected from one or more of vinyl dihydrogen phosphate, propylene dihydrogen phosphate, and vinylphosphonic acid.

[0018] Preferably, the aromatic monomer is selected from one or more of styrene, p-methylstyrene, and vinylnaphthalene.

[0019] Preferably, the nitrogen-containing heterocyclic monomer is selected from one or more of pyrrole, pyridine, and imidazole.

[0020] Preferably, in step 1), the organic solvent is selected from one or more of ethanol, methanol and isopropanol.

[0021] Preferably, the mass concentration of the aqueous solution is 20-30%.

[0022] Preferably, the mass concentration of the organic phase solution is 30-40%.

[0023] Preferably, in step 2), the heating conditions include: purging nitrogen gas into the aqueous solution for 20-40 minutes, raising the temperature to 60-80°C, and adjusting the stirring speed to 200-300 r / min.

[0024] Preferably, the initiator is ammonium persulfate and / or azobisisobutyronitrile.

[0025] Preferably, the amount of the initiator is 0.5 to 2% of the total monomer mass.

[0026] Preferably, the volume ratio of the organic phase solution to the initiator in the mixture of the organic phase solution and the initiator is 8~12:1.

[0027] Preferably, the polymerization reaction conditions include: adding the mixture of the organic phase solution and the initiator dropwise for 2-3 hours at a temperature of 60-80°C and a stirring speed of 200-300 r / min, and then maintaining the temperature for 4-6 hours.

[0028] Preferably, in step 3), the conditions for adjusting the pH include: adjusting the pH of the reaction product to 6.5-7.5 using sodium hydroxide solution, sodium bicarbonate solution or hydrochloric acid solution.

[0029] Preferably, the drying method is freeze drying.

[0030] Thirdly, the present invention provides an application of the functional carbon source as described in the present invention in the synthesis of lithium iron phosphate.

[0031] Fourthly, the present invention provides a method for preparing carbon-coated lithium iron phosphate, the method comprising the following steps: S1. A mixed slurry is prepared by mixing lithium iron phosphate precursor, functional carbon source, conventional carbon source and dispersion medium. S2. The mixed slurry is fed into a sand mill for sand milling, and then spray-dried to obtain lithium iron phosphate precursor powder; S3. The lithium iron phosphate precursor powder is pre-calcined and sintered in sequence under inert gas protection to obtain carbon-coated lithium iron phosphate. The functional carbon source is the functional carbon source described in this invention.

[0032] Preferably, in step S1, the dispersion medium is water and / or ethanol.

[0033] Preferably, in step S2, the conditions for sand milling include: the size of the zirconium beads in the sand mill is 0.4~0.8μm, the sand milling speed is 2000~2500r / min, and the sand milling time is 1~2.5h.

[0034] Preferably, in step S2, the conditions for spray drying include: an inlet air temperature of 180~220℃ and an outlet air temperature of 80~100℃.

[0035] Preferably, in step S3, the pre-firing conditions include: a temperature of 300~400℃ and a time of 1~3h.

[0036] Preferably, in step S3, the sintering conditions include: a temperature of 600~800℃ and a time of 3~8h.

[0037] Preferably, in step S3, the inert gas is nitrogen and / or argon.

[0038] Fifthly, the present invention provides a carbon-coated lithium iron phosphate main material prepared by the preparation method described in the present invention, wherein the carbon-coated lithium iron phosphate main material has a 0.1C specific capacity of 162~168 mAh / g and a 5C rate retention rate of 82~89%.

[0039] In the above technical solution, the functional carbon source of the present invention is a binary to pentagonal copolymer of five types of monomers: acrylic acid monomers, ammonium monomers, phosphate monomers, aromatic monomers, and nitrogen-containing heterocyclic monomers, with a molecular weight limited to 5000~50000 Da. The distribution of monomers in the molecular structure can be controlled by main chain-branch design to achieve targeted functional optimization. Combining acrylic acid monomers as the main chain and ammonium monomers as embedded main chains / branch chains, the carbon source utilizes the synergistic principle of reducing viscosity and dispersion with carboxyl groups in acrylic acid monomers, regulating charge with ammonium monomers, enhancing coating with coordination with phosphate monomers, increasing residual carbon with aromatic monomers, and conducting electricity with N-doping of nitrogen-containing heterocyclic monomers. This gives the carbon source both high dispersibility, high residual carbon rate, and excellent coating ability, solving the problem of single function of traditional carbon sources.

[0040] Meanwhile, the preparation method of the functional carbon source of the present invention involves the separation and formulation of water-soluble / oil-soluble monomer phases, and the polymerization method of first heating the hot water phase and then adding the organic phase-initiator mixture dropwise. The reaction temperature is controlled at 60~80℃, and the initiator dosage is 0.5~2%. Combined with pH 6.5~7.5 neutralization and freeze drying, the copolymerization reaction is ensured to be uniform, the molecular structure is controllable, the obtained carbon source has a stable molecular weight and no agglomeration, and the process is suitable for industrialization and produces no harmful waste.

[0041] Furthermore, the functional carbon source of the present invention is mixed with lithium iron phosphate precursors in a certain proportion. Relying on the high dispersibility of the carbon source, the slurry grinding solid content is significantly increased to 50-60%, the grinding time is shortened by 30-55%, and the slurry dispersion stability is excellent, with no viscosity abnormalities or agglomeration problems, ensuring production efficiency and product consistency.

[0042] Furthermore, by applying the functional carbon source of this invention to the synthesis of lithium iron phosphate, and through process optimization including milling with 0.4~0.8μm zirconium beads, spray drying at 180~220℃, pre-calcination at 300~400℃, and sintering at 600~800℃, the carbon source forms a uniform and dense N-doped carbon layer on the surface of lithium iron phosphate, constructing an efficient electron transport channel. The resulting carbon-coated lithium iron phosphate main material has a 0.1C specific capacity of 162~168mAh / g and a 5C rate retention rate of 82~89%, significantly improving electrochemical performance. Moreover, the entire process is compatible with existing lithium iron phosphate production systems, requiring no additional equipment modifications, and is easy to industrialize.

[0043] Other features and advantages of the present invention will be described in detail in the following detailed description section. Detailed Implementation

[0044] The following provides a detailed description of specific embodiments of the present invention. It should be understood that the specific embodiments described herein are for illustrative and explanatory purposes only and are not intended to limit the scope of the invention.

[0045] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0046] In a first aspect, the present invention provides a functional carbon source, which is polymerized from two or more of acrylic monomers, ammonium monomers, phosphate monomers, aromatic monomers and nitrogen-containing heterocyclic monomers; The number-average molecular weight of the functional carbon source is 5000~50000 Da.

[0047] The functional carbon source of this invention is a binary to pentagonal copolymer of five types of monomers: acrylic acid monomers, ammonium monomers, phosphate monomers, aromatic monomers, and nitrogen-containing heterocyclic monomers. The molecular weight is limited to 5000-50000 Da. The monomer distribution can be controlled through main-chain-branch design in the molecular structure to achieve targeted functional optimization. Combining acrylic acid monomers as the main chain and ammonium monomers as embedded main chains or branches, the invention utilizes the synergistic principle of carboxyl groups in acrylic acid monomers to reduce viscosity and dispersion, ammonium monomers to regulate charge, phosphate monomers to enhance coating through coordination, aromatic monomers to increase residual carbon, and nitrogen-containing heterocyclic monomers to promote conductivity through N-doping. This results in a carbon source that possesses high dispersibility, high residual carbon content, and excellent coating ability, solving the problem of single-function traditional carbon sources.

[0048] In this invention, the carboxyl groups in the acrylic monomers enhance dispersibility and reduce slurry viscosity, laying the foundation for high sand grinding content. They can serve as the main chain backbone or branched functional groups, and can be selected from one or more of acrylic acid, methacrylic acid, and ethyl acrylate.

[0049] In this invention, the cationic groups in the ammonium monomers regulate charge density, optimize dispersion stability, and decompose to produce gas during sintering to refine the pores of the carbon layer. They are mostly branched monomers, but can also be embedded in the main chain. For example, they can be selected from one or more of ammonium acrylate, methacrylamide, and dimethyl diallyl ammonium chloride.

[0050] In this invention, the phosphate group of the phosphate monomer coordinates with the hydroxyl group in the lithium iron phosphate precursor to enhance the carbon source binding force and improve the coating uniformity. It can be grafted onto the main chain or copolymer side chain, for example, it can be selected from one or more of ethylene dihydrogen phosphate, propylene dihydrogen phosphate and vinylphosphonic acid.

[0051] In this invention, the aromatic rings in the aromatic monomers increase the residual carbon ratio, construct electron transport channels, and can form copolymer branches or be embedded in the main chain. For example, they can be selected from one or more of styrene, p-methylstyrene, and vinylnaphthalene.

[0052] In this invention, the nitrogen atoms in the nitrogen-containing heterocyclic monomers achieve an N-doped carbon layer, reducing electron transport resistance and optimizing interface compatibility. They are often used as branched functional monomers, such as one or more selected from pyrrole, pyridine, and imidazole.

[0053] In this invention, by molar percentage, the functional carbon source comprises 20-45% acrylic acid monomers, 0-20% ammonium monomers, 0-18% phosphate monomers, 0-60% aromatic monomers, and 0-50% nitrogen-containing heterocyclic monomers; the sum of the molar percentages of each monomer is 100%.

[0054] Secondly, the present invention provides a method for preparing a functional carbon source as described in the present invention, the method comprising the following steps: 1) Dissolve water-soluble monomers in water to obtain an aqueous solution; dissolve oil-soluble monomers in an organic solvent to obtain an organic solution; 2) First, heat the aqueous solution, then add dropwise a mixture of organic solution and initiator to carry out the polymerization reaction, cool, adjust the pH, evaporate and concentrate, and dry to obtain a functional carbon source; The water-soluble monomer is selected from one or more of acrylic monomers, ammonium monomers, and phosphate monomers; The oil-soluble monomers are aromatic monomers and / or nitrogen-containing heterocyclic monomers.

[0055] The method for preparing the functional carbon source of the present invention involves separating and preparing water-soluble / oil-soluble monomer phases, and using a polymerization method of first heating the hot water phase and then adding the organic phase-initiator mixture dropwise. The reaction temperature is controlled at 60~80℃, and the amount of initiator is 0.5~2%. Combined with pH 6.5~7.5 neutralization and freeze drying, the copolymerization reaction is ensured to be uniform, the molecular structure is controllable, the obtained carbon source has a stable molecular weight and no agglomeration, and the process is suitable for industrialization and produces no harmful waste.

[0056] In this invention, the carboxyl groups in the acrylic monomers enhance dispersibility and reduce slurry viscosity, laying the foundation for high sand grinding content. They can serve as the main chain backbone or branched functional groups, and can be selected from one or more of acrylic acid, methacrylic acid, and ethyl acrylate.

[0057] In this invention, the cationic groups in the ammonium monomers regulate charge density, optimize dispersion stability, and decompose to produce gas during sintering to refine the pores of the carbon layer. They are mostly branched monomers, but can also be embedded in the main chain. For example, they can be selected from one or more of ammonium acrylate, methacrylamide, and dimethyl diallyl ammonium chloride.

[0058] In this invention, the phosphate group of the phosphate monomer coordinates with the hydroxyl group in the lithium iron phosphate precursor to enhance the carbon source binding force and improve the coating uniformity. It can be grafted onto the main chain or copolymer side chain, for example, it can be selected from one or more of ethylene dihydrogen phosphate, propylene dihydrogen phosphate and vinylphosphonic acid.

[0059] In this invention, the aromatic rings in the aromatic monomers increase the residual carbon ratio, construct electron transport channels, and can form copolymer branches or be embedded in the main chain. For example, they can be selected from one or more of styrene, p-methylstyrene, and vinylnaphthalene.

[0060] In this invention, the nitrogen atoms in the nitrogen-containing heterocyclic monomers achieve an N-doped carbon layer, reducing electron transport resistance and optimizing interface compatibility. They are often used as branched functional monomers, such as one or more selected from pyrrole, pyridine, and imidazole.

[0061] In this invention, in step 1), the organic solvent is not particularly limited and can be a conventional organic solvent in the art, such as one or more selected from ethanol, methanol and isopropanol.

[0062] In this invention, the mass concentration of the aqueous phase solution is 20-30%, and the mass concentration of the organic phase solution is 30-40%. Dissolving them separately first ensures complete dispersion of the monomers without agglomeration, avoiding uneven polymerization and an excessively wide molecular weight distribution caused by excessively high local concentrations.

[0063] In this invention, in step 2), the heating conditions include: purging the aqueous solution with nitrogen gas for 20-40 minutes, raising the temperature to 60-80°C, and adjusting the stirring speed to 200-300 r / min. Heating the aqueous phase first and purging it with nitrogen gas to remove oxygen helps stabilize the polymerization environment.

[0064] In this invention, the initiator is ammonium persulfate and / or azobisisobutyronitrile.

[0065] In this invention, the amount of the initiator is 0.5 to 2% of the total monomer mass.

[0066] In this invention, the volume ratio of the organic phase solution to the initiator in the mixture of the organic phase solution and the initiator is 8~12:1.

[0067] In this invention, the polymerization reaction conditions include: adding the mixture of the organic phase solution and the initiator dropwise for 2-3 hours at a temperature of 60-80°C and a stirring speed of 200-300 r / min, followed by maintaining the temperature for 4-6 hours. Slow dropwise addition controls the reaction rate and exothermic reaction.

[0068] In this invention, step 3) involves adjusting the pH of the reaction product to 6.5-7.5 using sodium hydroxide solution, sodium bicarbonate solution, or hydrochloric acid solution. This makes the polymer nearly neutral, improving its compatibility with the lithium iron phosphate precursor and making the slurry more stable.

[0069] In this invention, in order to overcome the defects of ordinary drying that easily leads to polymer adhesion and clumping, and damage to particle morphology, the drying method is freeze drying, which yields a loose, powdery carbon source with good flowability and faster and more uniform dispersion in slurry.

[0070] Thirdly, the present invention provides an application of the functional carbon source as described in the present invention in the synthesis of lithium iron phosphate.

[0071] Fourthly, the present invention provides a method for preparing carbon-coated lithium iron phosphate, the method comprising the following steps: S1. A mixed slurry is prepared by mixing lithium iron phosphate precursor, functional carbon source, conventional carbon source and dispersion medium. S2. The mixed slurry is fed into a sand mill for sand milling, and then spray-dried to obtain lithium iron phosphate precursor powder; S3. The lithium iron phosphate precursor powder is pre-calcined and sintered in sequence under inert gas protection to obtain carbon-coated lithium iron phosphate. The functional carbon source is the functional carbon source described in this invention.

[0072] The functional carbon source of this invention is applied to the synthesis of lithium iron phosphate. Through process optimization, including milling with 0.4~0.8μm zirconium beads, spray drying at 180~220℃, pre-calcination at 300~400℃, and sintering at 600~800℃, the carbon source forms a uniform and dense N-doped carbon layer on the surface of lithium iron phosphate, constructing an efficient electron transport channel. The resulting carbon-coated lithium iron phosphate main material has a 0.1C specific capacity of 162~168mAh / g and a 5C rate retention rate of 82~89%, significantly improving electrochemical performance. Moreover, the entire process is compatible with existing lithium iron phosphate production systems, requiring no additional equipment modifications and facilitating industrialization.

[0073] In this invention, in step S1, the dispersion medium is water and / or ethanol, and the conventional carbon source is selected from one or more of sucrose, glucose, starch, citric acid, polyvinyl alcohol and polyethylene glycol, preferably sucrose.

[0074] In this invention, the conditions for sand milling in step S2 include: the size of the zirconium beads in the sand mill is 0.4~0.8μm, the sand milling speed is 2000~2500r / min, and the sand milling time is 1~2.5h.

[0075] In this invention, the conditions for spray drying in step S2 include: an inlet air temperature of 180~220℃ and an outlet air temperature of 80~100℃.

[0076] In this invention, in step S3, in order to remove moisture and small molecule organic matter and avoid rapid gas generation and cracking during high-temperature sintering, the pre-firing conditions include: a temperature of 300~400℃ and a time of 1~3h.

[0077] In this invention, the sintering conditions in step S3 include a temperature of 600~800℃ and a time of 3~8h. This temperature allows the carbon source to fully pyrolyze and graphitize, while simultaneously completing the crystal growth of lithium iron phosphate, forming a continuous and uniform N-doped carbon coating layer.

[0078] In this invention, in step S3, the inert gas is nitrogen and / or argon.

[0079] Fifthly, the present invention provides a carbon-coated lithium iron phosphate main material prepared by the preparation method described in the present invention, wherein the carbon-coated lithium iron phosphate main material has a 0.1C specific capacity of 162~168 mAh / g and a 5C rate retention rate of 82~89%.

[0080] The present invention will be described in detail below through examples. In the following examples, the pharmaceuticals and agents are all conventional commercially available products.

[0081] In the following examples, m, n, p, q, and r all represent the degree of polymerization.

[0082] Example 1: Carbon source for acrylic acid-styrene binary copolymer 1. Monomer molar ratio: acrylic acid 40%, styrene 60%; Acrylic acid is the main chain, and styrene is embedded in the main chain, with a molecular weight of 8000 Da; 2. Molecular structural formula: -[CH2-CH(COOH)] m -[CH2-CH(C6H5)] n -,(m:n=2:3) 3. Synthesis method: a. Monomer pretreatment: Weigh 40 parts acrylic acid and 60 parts styrene by molar ratio; dissolve the acrylic acid in deionized water to prepare an aqueous solution with a mass concentration of 25%; dissolve the styrene in ethanol to prepare an organic solution with a mass concentration of 35%. b. Initiating copolymerization: Add the aqueous phase solution to the reactor, purge with nitrogen for 30 min to remove oxygen, raise the temperature to 70℃, and stir at 250 r / min; mix the organic phase solution with the initiator ammonium persulfate (1.0% of the total monomer mass) at a volume ratio of 10:1, and slowly add it dropwise to the reactor over 2.5 h. After the addition is complete, keep the reaction at the temperature for 5 h to regulate the main chain-branch structure. c. Post-processing: After the reaction is completed, cool to room temperature, adjust the pH to 7.0 with sodium hydroxide solution, concentrate by rotary evaporation to 1 / 3 of the original volume, and freeze-dry to obtain a solid powder product, namely the acrylic acid-styrene binary copolymer carbon source, denoted as B1.

[0083] Example 2: Carbon source for methacrylic acid-pyrrole binary copolymer 1. Monomer molar ratio: 50% methacrylic acid, 50% pyrrole; Methacrylic acid is the main chain, and pyrrole is grafted as the side chain, with a molecular weight of 10,000 Da. 2. Molecular structural formula: -[CH2-C(CH3)(COOH)] n -[-NH-C4H4N] m -,(n:m=1:1) 3. Synthesis method: a. Monomer pretreatment: Weigh 50 parts of methacrylic acid and 50 parts of pyrrole by molar ratio; dissolve the methacrylic acid in deionized water to prepare an aqueous solution with a mass concentration of 20%; dissolve the pyrrole in ethanol to prepare an organic solution with a mass concentration of 30%. b. Initiating copolymerization: Add the aqueous phase solution to the reactor, purge with nitrogen for 30 min to remove oxygen, raise the temperature to 65℃, and stir at 200 r / min; mix the organic phase solution with the initiator azobisisobutyronitrile (0.8% of the total monomer mass) at a volume ratio of 10:1, and slowly add it dropwise to the reactor over 2 h. After the addition is complete, keep the reaction at the temperature for 4.5 h to regulate the main chain-branch structure. c. Post-processing: After the reaction is completed, cool to room temperature, adjust the pH to 6.8 with sodium bicarbonate solution, concentrate by rotary evaporation to 1 / 3 of the original volume, and freeze-dry to obtain a solid powder product, namely the methacrylic acid-pyrrole binary copolymer carbon source, denoted as B2.

[0084] Example 3: Carbon source for acrylic acid-ammonium acrylate-styrene ternary copolymerization 1. Monomer molar ratio: acrylic acid 35%, ammonium acrylate 15%, styrene 50%; Acrylic acid is the main chain, ammonium acrylate and styrene are independent branches, and the molecular weight is 12000 Da. 2. Molecular structural formula: -[CH2-CH(COOH)] n -[-NH4OOC-CH=CH2] m -[-CH2-CH(C6H5)] p -,(n:m:p=7:3:10) 3. Synthesis method: a. Monomer pretreatment: Weigh out 35 parts acrylic acid, 15 parts ammonium acrylate, and 50 parts styrene by molar ratio; dissolve acrylic acid and ammonium acrylate in deionized water to prepare an aqueous solution with a mass concentration of 28%; dissolve styrene in ethanol to prepare an organic solution with a mass concentration of 38%. b. Initiating copolymerization: Add the aqueous phase solution to the reactor, purge with nitrogen for 30 min to remove oxygen, raise the temperature to 75℃, and stir at 280 r / min; mix the organic phase solution with the initiator ammonium persulfate (1.2% of the total monomer mass) at a volume ratio of 10:1, and slowly add it dropwise to the reactor over 3 h. After the addition is complete, keep the reaction at the temperature for 6 h to regulate the main chain-branch structure. c. Post-processing: After the reaction is completed, cool to room temperature, adjust the pH to 7.2 with hydrochloric acid solution, concentrate to 1 / 3 of the original volume by rotary evaporation, and freeze-dry to obtain a solid powder product, namely acrylic acid-ammonium acrylate-styrene ternary copolymer carbon source, denoted as B3.

[0085] Example 4: Carbon source for terpolymerization of methacrylate-ethylene dihydrogen phosphate-pyridine 1. Monomer molar ratio: 40% methacrylic acid, 10% ethylene dihydrogen phosphate, 50% pyridine; Methacrylic acid is the main chain, and diethylene phosphate-pyridine copolymer is the composite branch chain, with a molecular weight of 15,000 Da. 2. Molecular structural formula: -[CH2-C(CH3)(COOH)] n -[-OP(OH)2-CH=CH2-CH2-C5H4N] m -,(n:m=4:1) 3. Synthesis method: a. Monomer pretreatment: Weigh 40 parts methacrylic acid, 10 parts ethylene dihydrogen phosphate, and 50 parts pyridine by molar ratio; dissolve methacrylic acid and ethylene dihydrogen phosphate in deionized water to prepare an aqueous solution with a mass concentration of 22%; dissolve pyridine in ethanol to prepare an organic solution with a mass concentration of 32%. b. Initiating copolymerization: Add the aqueous phase solution to the reactor, purge with nitrogen for 30 min to remove oxygen, raise the temperature to 68℃, and stir at 220 r / min; mix the organic phase solution with the initiator azobisisobutyronitrile (1.5% of the total monomer mass) at a volume ratio of 10:1, and slowly add it dropwise to the reactor over 2.2 h. After the addition is complete, keep the reaction at the temperature for 4 h to regulate the main chain-branch structure. c. Post-processing: After the reaction is completed, cool to room temperature, adjust the pH to 6.6 with sodium hydroxide solution, concentrate to 1 / 3 of the original volume by rotary evaporation, and freeze-dry to obtain a solid powder product, namely the carbon source of methacrylate-ethylene dihydrogen phosphate-pyridine ternary copolymer, denoted as B4.

[0086] Example 5: Carbon source for ethyl acrylate-dimethyldiallylammonium chloride-vinylnaphthalene ternary copolymerization 1. Monomer molar ratio: Ethyl acrylate 30%, dimethyl diallyl ammonium chloride 20%, vinylnaphthalene 50%; Ethyl acrylate is the main chain, dimethyl diallyl ammonium chloride is the short branch chain, and vinyl naphthalene is the long branch chain, with a molecular weight of 18,000 Da. 2. Molecular structural formula: -[CH2-CH(COOC2H5)] n -[-N(CH3)2-C3H4] m -[-CH2-CH(C 10 H7)] p -,(n:m:p=3:2:5) 3. Synthesis method: a. Monomer pretreatment: Weigh out 30 parts of ethyl acrylate, 20 parts of dimethyl diallyl ammonium chloride, and 50 parts of vinyl naphthalene by molar ratio; dissolve ethyl acrylate and dimethyl diallyl ammonium chloride in deionized water to prepare an aqueous solution with a mass concentration of 30%; dissolve vinyl naphthalene in ethanol to prepare an organic solution with a mass concentration of 40%. b. Initiating copolymerization: Add the aqueous phase solution to the reactor, purge with nitrogen for 30 min to remove oxygen, raise the temperature to 80℃, and stir at 300 r / min; mix the organic phase solution with the initiator ammonium persulfate (2.0% of the total monomer mass) at a volume ratio of 10:1, and slowly add it dropwise to the reactor over a period of 2.8 h. After the addition is complete, keep the reaction at the temperature for 5.5 h to regulate the main chain-branch structure. c. Post-processing: After the reaction is completed, cool to room temperature, adjust the pH to 7.4 with hydrochloric acid solution, concentrate to 1 / 3 of the original volume by rotary evaporation, and freeze-dry to obtain a solid powder product, namely ethyl acrylate-dimethyl diallyl ammonium chloride-vinyl naphthalene ternary copolymer carbon source, denoted as B5.

[0087] Example 6: Carbon source for terpolymerization of acrylic acid-propylene dihydrogen phosphate-styrene 1. Monomer molar ratio: acrylic acid 45%, propylene dihydrogen phosphate 5%, styrene 50%; Acrylic acid-styrene main chain, with dihydropropylene phosphate grafted onto aromatic ring, molecular weight 9000 Da; 2. Molecular structural formula: -[CH2-CH(COOH)] n -[CH2-CH(C6H4-OP(OH)2)] m -[CH2-CH(C6H5)] p -,(n:m:p)=(9:1:10); 3. Synthesis method: a. Monomer pretreatment: Weigh out 45 parts acrylic acid, 5 parts propylene dihydrogen phosphate, and 50 parts styrene by molar ratio; dissolve acrylic acid and propylene dihydrogen phosphate in deionized water to prepare an aqueous solution with a mass concentration of 24%; dissolve styrene in ethanol to prepare an organic solution with a mass concentration of 36%. b. Initiation of copolymerization: Add the aqueous phase solution to the reactor, purge with nitrogen for 30 min to remove oxygen, raise the temperature to 62℃, and stir at 240 r / min; mix the organic phase solution with the initiator azobisisobutyronitrile (0.6% of the total monomer mass) at a volume ratio of 10:1, and slowly add it dropwise to the reactor over a period of 2.1 h. After the addition is complete, keep the reaction at the temperature for 4.2 h to regulate the main chain-branch structure. c. Post-processing: After the reaction is completed, cool to room temperature, adjust the pH to 6.9 with sodium bicarbonate solution, concentrate to 1 / 3 of the original volume by rotary evaporation, and freeze-dry to obtain a solid powder product, namely the terpolymer carbon source of acrylic acid-dihydropropylene phosphate-styrene, denoted as B6.

[0088] Example 7: Acrylic acid-ammonium acrylate-styrene-pyrrole quaternary copolymer carbon source 1. Monomer molar ratio: acrylic acid 30%, ammonium acrylate 15%, styrene 35%, pyrrole 20%; Acrylic acid is the main chain, and the other three are independent branches, with a molecular weight of 20,000 Da. 2. Molecular structural formula: -[CH2-CH(COOH)] n -[-NH4OOC-CH=CH2]m-[-CH2-CH(C6H5)] p -[-NH-C4H4N] q -,(n:m:p:q=6:3:7:4) 3. Synthesis method: a. Monomer pretreatment: Weigh out 30 parts acrylic acid, 15 parts ammonium acrylate, 35 parts styrene, and 20 parts pyrrole by molar ratio; dissolve acrylic acid and ammonium acrylate in deionized water to prepare an aqueous solution with a mass concentration of 26%; dissolve styrene and pyrrole in ethanol to prepare an organic solution with a mass concentration of 34%. b. Initiating copolymerization: Add the aqueous phase solution to the reactor, purge with nitrogen for 30 min to remove oxygen, raise the temperature to 72℃, and stir at 260 r / min; mix the organic phase solution with the initiator ammonium persulfate (1.1% of the total monomer mass) at a volume ratio of 10:1, and slowly add it dropwise to the reactor over a period of 2.6 h. After the addition is complete, keep the reaction at the temperature for 5.2 h to regulate the main chain-branch structure. c. Post-processing: After the reaction is completed, cool to room temperature, adjust the pH to 7.1 with sodium hydroxide solution, concentrate to 1 / 3 of the original volume by rotary evaporation, and freeze-dry to obtain a solid powder product, namely acrylic acid-ammonium acrylate-styrene-pyrrole quaternary copolymer carbon source, denoted as B7.

[0089] Example 8: Carbon source for quaternary copolymerization of methacrylic acid-ammonium acrylate-vinyl dihydrogen phosphate-styrene 1. Monomer molar ratio: 25% methacrylic acid, 15% ammonium acrylate, 10% vinyl dihydrogen phosphate, 50% styrene; Methacrylic acid is the main chain, ammonium acrylate-ethylene dihydrogen phosphate is the complex branch chain, and styrene is the independent branch chain, with a molecular weight of 22000 Da. 2. Molecular structural formula: -[CH2-C(CH2)(COOH)] n -[-NH4OOC-CH=CH2-OP(OH)2] m -[-CH2-CH(C6H5)] p -,(n:m:p=5:3:10) 3. Synthesis method: a. Monomer pretreatment: Weigh 25 parts methacrylic acid, 15 parts ammonium acrylate, 10 parts ethylene dihydrogen phosphate, and 50 parts styrene by molar ratio; dissolve methacrylic acid, ammonium acrylate, and ethylene dihydrogen phosphate in deionized water to prepare an aqueous solution with a mass concentration of 27%; dissolve styrene in ethanol to prepare an organic solution with a mass concentration of 37%. b. Initiating copolymerization: Add the aqueous phase solution to the reactor, purge with nitrogen for 30 min to remove oxygen, raise the temperature to 76℃, and stir at 270 r / min; mix the organic phase solution with the initiator ammonium persulfate (1.3% of the total monomer mass) at a volume ratio of 10:1, and slowly add it dropwise to the reactor over a period of 2.9 h. After the addition is complete, keep the reaction at the temperature for 5.8 h to regulate the main chain-branch structure. c. Post-processing: After the reaction is completed, cool to room temperature, adjust the pH to 7.3 with hydrochloric acid solution, concentrate to 1 / 3 of the original volume by rotary evaporation, and freeze-dry to obtain a solid powder product, namely acrylic acid-ammonium acrylate-styrene-pyrrole quaternary copolymer carbon source, denoted as B8.

[0090] Example 9: Acrylic acid-diallylammonium chloride-propylene dihydrogen phosphate-pyridine quaternary copolymer carbon source 1. Monomer molar ratio: acrylic acid 35%, dimethyl diallyl ammonium chloride 15%, dihydropropylene phosphate 10%, pyridine 40%; Acrylic acid is the main chain, dimethyl diallyl ammonium chloride is a short branch chain, and dihydropropylene phosphate-pyridine is a long branch chain, with a molecular weight of 21,000 Da. 2. Molecular structural formula: -[CH2-CH(COOH)] n -[-N(CH3)2-C3H4] m -[-OP(OH)2-CH=CH2-CH2-C5H4N] p -,(n:m:p=7:3:8) 3. Synthesis method: a. Monomer pretreatment: Weigh out 35 parts acrylic acid, 15 parts dimethyl diallyl ammonium chloride, 10 parts dihydropropylene phosphate, and 40 parts pyridine by molar ratio; dissolve acrylic acid, dimethyl diallyl ammonium chloride, and dihydropropylene phosphate in deionized water to prepare an aqueous solution with a mass concentration of 23%; dissolve pyridine in ethanol to prepare an organic solution with a mass concentration of 33%. b. Initiation of copolymerization: Add the aqueous phase solution to the reactor, purge with nitrogen for 30 min to remove oxygen, raise the temperature to 66℃, and stir at 230 r / min; mix the organic phase solution with the initiator azobisisobutyronitrile (1.4% of the total monomer mass) at a volume ratio of 10:1, and slowly add it dropwise to the reactor over 2.3 h. After the addition is complete, keep the reaction at the temperature for 4.3 h to regulate the main chain-branch structure. c. Post-processing: After the reaction is completed, cool to room temperature, adjust the pH to 6.7 with sodium bicarbonate solution, concentrate to 1 / 3 of the original volume by rotary evaporation, and freeze-dry to obtain a solid powder product, namely acrylic acid-dimethyl diallyl ammonium chloride-dihydropropylene phosphate-pyridine quaternary copolymer carbon source, denoted as B9.

[0091] Example 10: Ethyl acrylate-methacrylamide-vinylnaphthalene-imidazolium quaternary copolymer carbon source 1. Monomer molar ratio: Ethyl acrylate 20%, Methacrylamide 20%, Vinylnaphthalene 30%, Imidazole 30%; Ethyl acrylate-methacrylamide as the main chain, vinylnaphthalene-imidazolium as the complex branch chain, with a molecular weight of 25,000 Da; 2. Molecular structural formula: -[CH2-CH(COOC2H5)] n -[CH2-C(CH3)(CONH2)] m -[CH2-CH(C 10 H7)-CH2-C3H4N2] p -,(n:m:p=2:2:6); 3. Synthesis method: a. Monomer pretreatment: Weigh out 20 parts of ethyl acrylate, 20 parts of methacrylamide, 30 parts of vinylnaphthalene, and 30 parts of imidazole by molar ratio; dissolve ethyl acrylate and methacrylamide in deionized water to prepare an aqueous solution with a mass concentration of 29%; dissolve vinylnaphthalene and imidazole in ethanol to prepare an organic solution with a mass concentration of 39%. b. Initiation of copolymerization: Add the aqueous phase solution to the reactor, purge with nitrogen for 30 min to remove oxygen, raise the temperature to 78℃, and stir at 290 r / min; mix the organic phase solution with the initiator azobisisobutyronitrile (1.8% of the total monomer mass) at a volume ratio of 10:1, and slowly add it dropwise to the reactor over a period of 2.7 h. After the addition is complete, keep the reaction at the temperature for 5.6 h to regulate the main chain-branch structure. c. Post-processing: After the reaction is completed, cool to room temperature, adjust the pH to 7.4 with hydrochloric acid solution, concentrate by rotary evaporation to 1 / 3 of the original volume, and freeze-dry to obtain a solid powder product, namely ethyl acrylate-methacrylamide-vinylnaphthalene-imidazolium quaternary copolymer carbon source, denoted as B10.

[0092] Example 11: Carbon source for acrylate-ethylene dihydrogen phosphate-styrene-pyridine quaternary copolymer 1. Monomer molar ratio: acrylic acid 30%, vinyl dihydrogen phosphate 10%, styrene 40%, pyridine 20%; Acrylic acid-styrene main chain, ethylene dihydrogen phosphate, and pyridine are independent branches, with a molecular weight of 16,000 Da. 2. Molecular structural formula: -[CH2-CH(COOH)] n -[CH2-CH(C6H6)] m -[CH2-CH(OP(OH)2)] p -[CH2-C5H4N] q -(n:m:p:q=3:4:1:2); 3. Synthesis method: a. Monomer pretreatment: Weigh out 30 parts acrylic acid, 10 parts ethylene dihydrogen phosphate, 40 parts styrene, and 20 parts pyridine by molar ratio; dissolve acrylic acid and ethylene dihydrogen phosphate in deionized water to prepare an aqueous solution with a mass concentration of 25%; dissolve styrene and pyridine in ethanol to prepare an organic solution with a mass concentration of 35%. b. Initiation of copolymerization: Add the aqueous phase solution to the reactor, purge with nitrogen for 30 min to remove oxygen, raise the temperature to 69℃, and stir at 250 r / min; mix the organic phase solution with the initiator azobisisobutyronitrile (0.9% of the total monomer mass) at a volume ratio of 10:1, and slowly add it dropwise to the reactor over 2.4 h. After the addition is complete, keep the reaction at the temperature for 4.8 h to regulate the main chain-branch structure. c. Post-processing: After the reaction is completed, cool to room temperature, adjust the pH to 7.0 with sodium hydroxide solution, concentrate by rotary evaporation to 1 / 3 of the original volume, and freeze-dry to obtain a solid powder product, namely the quaternary copolymer carbon source of acrylate-ethylene dihydrogen phosphate-styrene-pyridine, denoted as B11.

[0093] Example 12: Five-element balanced carbon source 1. Monomer molar ratio: acrylic acid 30%, ammonium acrylate 15%, vinyl dihydrogen phosphate 10%, styrene 25%, pyrrole 20%; Acrylic acid is the main chain, and the other four are independent branches, with a molecular weight of 23,000 Da. 2. Molecular structural formula: -[CH2-CH(COOH)] n -[-NH4OOC-CH=CH2] m -[-OP(OH)2-CH=CH2] p -[-CH2-CH(C6H5)] q -[-NH-C4H4N] r -, (n:m:p:q:r=6:3:2:5:4); 3. Synthesis method: a. Monomer pretreatment: Weigh out 30 parts acrylic acid, 15 parts ammonium acrylate, 10 parts ethylene dihydrogen phosphate, 25 parts styrene, and 20 parts pyrrole by molar ratio; dissolve acrylic acid, ammonium acrylate, and ethylene dihydrogen phosphate in deionized water to prepare an aqueous solution with a mass concentration of 26%; dissolve styrene and pyrrole in ethanol to prepare an organic solution with a mass concentration of 34%. b. Initiating copolymerization: Add the aqueous phase solution to the reactor, purge with nitrogen for 30 min to remove oxygen, raise the temperature to 71℃, and stir at 260 r / min; mix the organic phase solution with the initiator ammonium persulfate (1.2% of the total monomer mass) at a volume ratio of 10:1, and slowly add it dropwise to the reactor over 2.5 h. After the addition is complete, keep the reaction at the temperature for 5.1 h to regulate the main chain-branch structure. c. Post-processing: After the reaction is completed, cool to room temperature, adjust the pH to 6.9 with sodium bicarbonate solution, concentrate to 1 / 3 of the original volume by rotary evaporation, and freeze-dry to obtain a solid powder product, namely a balanced five-element functional carbon source, denoted as B12.

[0094] Example 13: Five-element carbon source of high acrylic acid monomer 1. Monomer molar ratio: acrylic acid 40%, ammonium acrylate 10%, vinyl dihydrogen phosphate 8%, styrene 22%, pyrrole 20%; The main chain is high-proportion acrylic acid, and the ammonium acrylate side chain is shorter compared to Example 12, with a molecular weight of 24000 Da. 2. Molecular structural formula: -[CH2-CH(COOH)] n -[-NH4OOC-CH=CH2] m -[-OP(OH)2-CH=CH2] p -[-CH2-CH(C6H5)] q -[-NH-C4H4N] r-, (n:m:p:q:r=4:1:0.8:2.2:2); 3. Synthesis method: a. Monomer pretreatment: Weigh out 40 parts acrylic acid, 10 parts ammonium acrylate, 8 parts ethylene dihydrogen phosphate, 22 parts styrene, and 20 parts pyrrole by molar ratio; dissolve acrylic acid, ammonium acrylate, and ethylene dihydrogen phosphate in deionized water to prepare an aqueous solution with a mass concentration of 27%; dissolve styrene and pyrrole in ethanol to prepare an organic solution with a mass concentration of 36%. b. Initiating copolymerization: Add the aqueous phase solution to the reactor, purge with nitrogen for 30 min to remove oxygen, raise the temperature to 73℃, and stir at 270 r / min; mix the organic phase solution with the initiator ammonium persulfate (1.3% of the total monomer mass) at a volume ratio of 10:1, and slowly add it dropwise to the reactor over a period of 2.6 h. After the addition is complete, keep the reaction at the temperature for 5.3 h to regulate the main chain-branch structure. c. Post-processing: After the reaction is completed, cool to room temperature, adjust the pH to 7.2 with hydrochloric acid solution, concentrate to 1 / 3 of the original volume by rotary evaporation, and freeze-dry to obtain a solid powder product, namely a high-acrylic acid monomer five-membered carbon source, denoted as B13.

[0095] Example 14: Five-membered carbon source of high nitrogen-containing heterocyclic monomer 1. Monomer molar ratio: acrylic acid 25%, ammonium acrylate 15%, propylene dihydrogen phosphate 10%, styrene 25%, imidazole 25%; Acrylic acid is the main chain, ammonium acrylate is an independent branch, dihydropropylene phosphate-styrene is a complex branch, the density of imidazole branch is increased, and the molecular weight is 26000 Da. 2. Molecular structural formula: -[CH2-CH(COOH)] n -[-NH4OOC-CH=CH2] m -[-OP(OH)2-CH=CH2-CH2-CH(C6H5)] p -[-C3H4N2] q -,(n:m:p:q=5:3:5:5) 3. Synthesis method: a. Monomer pretreatment: Weigh out 25 parts acrylic acid, 15 parts ammonium acrylate, 10 parts dihydropropylene phosphate, 25 parts styrene, and 25 parts imidazole by molar ratio; dissolve acrylic acid, ammonium acrylate, and dihydropropylene phosphate in deionized water to prepare an aqueous solution with a mass concentration of 24%; dissolve styrene and imidazole in ethanol to prepare an organic solution with a mass concentration of 35%. b. Initiation of copolymerization: Add the aqueous phase solution to the reactor, purge with nitrogen for 30 min to remove oxygen, raise the temperature to 74℃, and stir at 280 r / min; mix the organic phase solution with the initiator azobisisobutyronitrile (1.6% of the total monomer mass) at a volume ratio of 10:1, and slowly add it dropwise to the reactor over a period of 2.7 h. After the addition is complete, keep the reaction at the temperature for 5.4 h to regulate the main chain-branch structure. c. Post-processing: After the reaction is completed, cool to room temperature, adjust the pH to 7.1 with sodium hydroxide solution, concentrate to 1 / 3 of the original volume by rotary evaporation, and freeze-dry to obtain a solid powder product, namely a five-membered carbon source of high nitrogen-containing heterocyclic monomer, denoted as B14.

[0096] Example 15: Five-membered carbon source for high aromatic hydrocarbon monomers 1. Monomer molar ratio: acrylic acid 20%, dimethyl diallyl ammonium chloride 15%, dihydropropylene phosphate 10%, vinylnaphthalene 35%, pyridine 20%; Acrylic acid is the main chain, dimethyl diallyl ammonium chloride is the short branch chain, dihydropropylene phosphate-pyridine is the complex branch chain, vinyl naphthalene is the long branch chain, and the molecular weight is 27000 Da. 2. Molecular structural formula: -[CH2-CH(COOH)] n -[-N(CH3)2-C3H4] m -[-OP(OH)2-CH=CH2-CH2-C5H4N] p -[-CH2-CH(C 10 H7)] q -,(n:m:p:q=4:3:6:7); 3. Synthesis method: a. Monomer pretreatment: Weigh out 20 parts acrylic acid, 15 parts dimethyl diallyl ammonium chloride, 10 parts dihydropropylene phosphate, 35 parts vinylnaphthalene, and 20 parts pyridine by molar ratio; dissolve acrylic acid, dimethyl diallyl ammonium chloride, and dihydropropylene phosphate in deionized water to prepare an aqueous solution with a mass concentration of 28%; dissolve vinylnaphthalene and pyridine in ethanol to prepare an organic solution with a mass concentration of 38%. b. Initiating copolymerization: Add the aqueous phase solution to the reactor, purge with nitrogen for 30 min to remove oxygen, raise the temperature to 76℃, and stir at 290 r / min; mix the organic phase solution with the initiator ammonium persulfate (1.7% of the total monomer mass) at a volume ratio of 10:1, and slowly add it dropwise to the reactor over 2.8 h. After the addition is complete, keep the reaction at the temperature for 5.5 h to regulate the main chain-branch structure. c. Post-processing: After the reaction is completed, cool to room temperature, adjust the pH to 7.3 with hydrochloric acid solution, concentrate to 1 / 3 of the original volume by rotary evaporation, and freeze-dry to obtain a solid powder product, namely the five-membered carbon source of high aromatic hydrocarbon monomer, denoted as B15.

[0097] Example 16: High-phosphate monomeric five-element carbon source 1. Monomer molar ratio: acrylic acid 25%, ammonium acrylate 15%, vinyl dihydrogen phosphate 18%, styrene 22%, imidazole 20%; Acrylic acid is the main chain, ethylene dihydrogen phosphate is a long branched chain, and the other three are independent short branches, with a molecular weight of 25,000 Da. 2. Molecular structural formula: -[CH2-CH(COOH)] n -[-NH4OOC-CH=CH2] m -[-OP(OH)2-CH=CH2] p -[-CH2-CH(C6H5)] q -[-C3H4N2] r -, (n:m:p:q:r=5:3:3.6:4.4:4); 3. Synthesis method: a. Monomer pretreatment: Weigh out 25 parts acrylic acid, 15 parts ammonium acrylate, 18 parts ethylene dihydrogen phosphate, 22 parts styrene, and 20 parts imidazole by molar ratio; dissolve acrylic acid, ammonium acrylate, and ethylene dihydrogen phosphate in deionized water to prepare an aqueous solution with a mass concentration of 25%; dissolve styrene and imidazole in ethanol to prepare an organic solution with a mass concentration of 36%. b. Initiation of copolymerization: Add the aqueous phase solution to the reactor, purge with nitrogen for 30 min to remove oxygen, raise the temperature to 70℃, and stir at 260 r / min; mix the organic phase solution with the initiator azobisisobutyronitrile (1.5% of the total monomer mass) at a volume ratio of 10:1, and slowly add it dropwise to the reactor over a period of 2.6 h. After the addition is complete, keep the reaction at the temperature for 5.2 h to regulate the main chain-branch structure. c. Post-processing: After the reaction is completed, cool to room temperature, adjust the pH to 6.8 with sodium bicarbonate solution, concentrate to 1 / 3 of the original volume by rotary evaporation, and freeze-dry to obtain a solid powder product, namely a high-phosphate monomer five-membered carbon source, denoted as B16.

[0098] Example 17: Five-element carbon source with low functional monomer content 1. Monomer molar ratio: acrylic acid 35%, ammonium acrylate 10%, propylene dihydrogen phosphate 5%, styrene 30%, pyrrole 20%; Acrylic acid is the main chain, and the other monomers are short-chained with a molecular weight of 22,000 Da. 2. Molecular structural formula: -[CH2-CH(COOH)] m -[-NH4OOC-CH=CH2] n -[-OP(OH)2-CH=CH2] p-[-CH2-CH(C6H5)] q -[-NH-C4H4N] r -,(m:n:p:q:r=7:2:1:6:4); 3. Synthesis method: a. Monomer pretreatment: Weigh out 35 parts acrylic acid, 10 parts ammonium acrylate, 5 parts dihydropropylene phosphate, 30 parts styrene, and 20 parts pyrrole by molar ratio; dissolve acrylic acid, ammonium acrylate, and dihydropropylene phosphate in deionized water to prepare an aqueous solution with a mass concentration of 23%; dissolve styrene and pyrrole in ethanol to prepare an organic solution with a mass concentration of 34%. b. Initiating copolymerization: Add the aqueous phase solution to the reactor, purge with nitrogen for 30 min to remove oxygen, raise the temperature to 68℃, and stir at 250 r / min; mix the organic phase solution with the initiator ammonium persulfate (1.1% of the total monomer mass) at a volume ratio of 10:1, and slowly add it dropwise to the reactor over 2.4 h. After the addition is complete, keep the reaction at the temperature for 4.9 h to regulate the main chain-branch structure. c. Post-processing: After the reaction is completed, cool to room temperature, adjust the pH to 7.0 with sodium hydroxide solution, concentrate by rotary evaporation to 1 / 3 of the original volume, and freeze-dry to obtain a solid powder product, namely a low-functional monomer ratio five-membered carbon source, denoted as B17.

[0099] Application Example 1 S1. Preparation of lithium iron phosphate precursor mixed slurry: Weigh the lithium iron phosphate precursor, the functional carbon source prepared in Example 1, sucrose and deionized water according to the mass ratio of 40:0.4:10:49.6; put the weighed raw materials into a mixing tank and stir at 300 r / min for 60 min at room temperature until the components are evenly dispersed and there is no agglomeration, to obtain the lithium iron phosphate precursor mixed slurry.

[0100] S2. Sand milling and refining treatment: The lithium iron phosphate precursor mixture slurry from step S1 is transferred to a horizontal sand mill. Zirconia beads with a particle size of 0.4~0.8μm are selected as the grinding medium. The speed of the sand mill is adjusted to 2200r / min, and sand milling is carried out at a constant temperature for 1.8h until the particle size D50 of the slurry reaches 0.5±0.1μm. The sand milling and dispersion are completed, and the material is discharged for later use.

[0101] S3. Spray drying and granulation: The qualified slurry from step S2 is fed into a centrifugal spray dryer. The process parameters are set as follows: inlet air temperature 200℃, outlet air temperature 90℃, and feed rate 5mL / min. Spray drying is performed to obtain lithium iron phosphate precursor powder with good flowability and uniform particle size.

[0102] S4. Inert atmosphere pre-calcination: Transfer the lithium iron phosphate precursor powder from step S3 to a tube sintering furnace, continuously introduce nitrogen as a protective gas, and exhaust the air in the furnace for 30 minutes; raise the temperature to 350°C at a heating rate of 5°C / min, hold for 2 hours to complete the pre-calcination, remove moisture, residual organic solvents and small molecule organic impurities from the slurry, and initially form a loose carbon coating layer.

[0103] S5. High-temperature sintering: After the pre-firing in step S4, the nitrogen atmosphere is kept constant, and the temperature is raised to 750°C at a rate of 8°C / min. The temperature is held for 5 hours for high-temperature sintering. During the sintering process, the functional carbon source is pyrolyzed to form a continuous and dense nitrogen-doped carbon coating layer. At the same time, the lithium iron phosphate precursor completes crystal reconstruction and structural improvement. After sintering, the furnace is cooled to room temperature, and the carbon-coated lithium iron phosphate material is obtained by unloading, which is denoted as Y1.

[0104] Application Example 2-17 Application Examples 2-17 correspond to the functional carbon sources prepared in Examples 2-17. Except for replacing the functional carbon source, the other raw material ratios, process parameters and operating steps are completely consistent with Application Example 1. Corresponding carbon-coated lithium iron phosphate materials were prepared in sequence and denoted as Y2~Y17.

[0105] Detection Example 1 The lithium iron phosphate precursor mixture slurry and carbon-coated lithium iron phosphate material prepared for corresponding use cases 1-17 were tested for performance using the following methods, and the results are shown in Table 1: 1. Sand milling solids content test: The gravimetric method was used. 10g of the sand milled slurry was placed in an oven at 105℃ and dried to constant weight. The percentage of the solids mass after drying to the initial mass of the slurry was calculated. 2. Sand milling time test: The time required from starting the sand mill to reaching the particle size of D50=0.5±0.1μm was recorded as the endpoint. 3. Residual carbon rate test: Thermogravimetric analysis (TGA) was used. 5 mg of functional carbon source sample was taken and heated from room temperature to 800℃ at a heating rate of 10℃ / min under nitrogen atmosphere, and kept at this temperature for 2 hours. The percentage of the remaining solid mass to the initial mass of the sample was calculated. 4. 0.1C capacity test: The carbon-coated lithium iron phosphate main material was mixed with acetylene black and polyvinylidene fluoride (PVDF) at a mass ratio of 97:2:1. N-methylpyrrolidone (NMP) was added to form a slurry, which was then coated onto copper foil and dried to form a coin cell. A constant current charge-discharge test was performed at a 0.1C rate, with a charging voltage of 3.6V and a discharging voltage of 2.0V. The first discharge capacity was recorded and divided by the mass of the active material. 5. 5C Rate Retention Rate Test: Using the above-mentioned button cell battery, first activate the battery by charging and discharging it 3 times at a 0.1C rate, then discharge it at a 5C rate and charge it at a 0.1C rate, repeating this cycle 50 times. Record the percentage of the discharge capacity on the 50th discharge cycle to the initial 0.1C discharge capacity.

[0106] Table 1

[0107] As can be seen from the above content and the data in Table 1, the functional carbon source prepared in Example 1 contains only two monomers, resulting in a single function. The carboxyl group of acrylic acid provides basic dispersibility, making the solid content of the slurry prepared in Example 1 superior to that of traditional carbon sources. However, the lack of ammonium monomers to regulate charge with cations limits the dispersion efficiency, thus requiring a longer milling time. The aromatic ring structure of styrene improves the residual carbon rate, providing a basis for conductivity. However, the lack of nitrogen-containing heterocyclic monomers for N doping results in greater electron transport resistance, leading to mediocre rate performance. Furthermore, the absence of phosphate monomers weakens the binding force between the carbon source and the lithium iron phosphate precursor, resulting in insufficient carbon coating uniformity and a specific capacity that does not reach a high-order level.

[0108] In Example 2, the carboxyl group of methacrylic acid in the functional carbon source has greater steric hindrance than that of acrylic acid, resulting in slightly better dispersion stability. Therefore, the solid content of the prepared slurry is slightly higher than that in Application Example 1, and the milling time is slightly shorter. Pyrrole, as a nitrogen-containing heterocyclic monomer, forms an N-doped carbon layer after grafting, reducing electron transport resistance and resulting in better rate performance than in Example 1. However, the lack of aromatic monomers leads to insufficient aromatic ring structure, resulting in a 0.5% lower residual carbon content than the functional carbon source prepared in Example 1, and poor carbon layer density. The absence of ammonium monomers to optimize charge balance limits the improvement in dispersion performance. The lack of phosphate monomers to enhance interfacial bonding makes local vacancies easily appear in carbon coating, limiting the increase in specific capacity.

[0109] Compared to the binary functional carbon sources prepared in Examples 1-2, the functional carbon source prepared in Example 3 contains an additional ammonium monomer, ammonium acrylate, which synergistically interacts with acrylic acid. The carboxyl group of acrylic acid provides the dispersion basis, while the ammonium acrylate cation regulates the charge density, reduces the slurry viscosity, and significantly improves dispersion stability. Consequently, the solid content is increased to 55%, and the milling time is shortened to 1.6 hours. With a styrene content of 50%, the aromatic ring structure is sufficient, the residual carbon rate is increased to 9.1%, and the continuity of the carbon layer is optimized. However, it lacks nitrogen-containing heterocyclic monomers and has no N-doping modification, resulting in lower electron transport efficiency than the carbon-coated lithium iron phosphate material prepared in Example 2, and slightly inferior rate performance. Furthermore, the lack of phosphate monomers means that the carbon source and precursor are only bound by intermolecular forces, which are weaker than those of phosphate-containing systems. This results in localized uneven carbon coating and a slightly lower specific capacity than the carbon-coated lithium iron phosphate material prepared in Example 2.

[0110] The functional carbon source prepared in Example 4 incorporates a new phosphate monomer, ethylene dihydrogen phosphate. Its phosphate groups form coordination bonds with the hydroxyl groups on the surface of the lithium iron phosphate precursor, significantly enhancing the binding force between the carbon source and the precursor. This results in a marked improvement in carbon coating uniformity, making it the best specific capacity among ternary functional carbon sources. Pyridine, as a nitrogen-containing heterocyclic monomer, copolymerizes with phosphate to form a composite branch, with N doping and interfacial bonding synergistically optimized, resulting in optimal rate performance. However, the absence of ammonium monomers and the lack of cation-mediated charge regulation means that dispersion performance relies solely on the carboxyl groups of methacrylic acid. Consequently, the solid content is lower than the slurry prepared in Application Example 3, requiring a longer milling time. The absence of aromatic monomers also results in a lower residual carbon content compared to the carbon-coated lithium iron phosphate material prepared in Application Example 3, leading to insufficient carbon layer density and limiting further improvements in specific capacity and rate performance.

[0111] In Example 5, the functional carbon source ammonium monomer was selected as dimethyl diallyl ammonium chloride, which has higher cationic activity than ammonium acrylate. It synergistically regulates charge with the ester group of ethyl acrylate, resulting in optimal dispersion performance and a solid content of 56% with the shortest milling time. The aromatic monomer was selected as vinylnaphthalene, which has more aromatic rings than styrene, exhibiting stronger thermal stability and a carbon residue rate of 10.2%, the highest among ternary functional carbon sources, with the best carbon layer continuity. However, the lack of nitrogen-containing heterocyclic monomers and the absence of N-doping modification resulted in higher electron transport resistance and lower rate performance compared to the carbon-coated lithium iron phosphate material prepared in Example 4. The absence of phosphate monomers also weakened the binding force between the carbon source and the precursor, making the carbon coating prone to detachment and resulting in a lower specific capacity than the carbon-coated lithium iron phosphate material prepared in Example 4.

[0112] The functional carbon source prepared in Example 6 contains the phosphate monomer dihydropropylene phosphate, but its proportion is only 5%, resulting in weak coordination and limited carbon coating optimization effect. Lacking ammonium monomers, its dispersion performance depends solely on the carboxyl group of acrylic acid. Therefore, its solid content and milling time are similar to the slurry prepared in Application Example 2, superior to the slurry prepared in Application Example 4 (which lacks ammonium monomers), but weaker than the slurries prepared in Application Examples 3 and 5 (which contain ammonium monomers). With a styrene content of 50% and a residual carbon rate of 9.3%, slightly higher than the carbon-coated lithium iron phosphate material prepared in Application Example 3, but lacking nitrogen-containing heterocyclic compounds, its rate performance is comparable to that of the carbon-coated lithium iron phosphate material prepared in Application Example 3. The excessively high proportion of acrylic acid (45%) crowds out the space for functional monomers, resulting in balanced overall performance without any outstanding advantages.

[0113] The functional carbon source prepared in Example 7 integrates three types of functional monomers: dispersion (acrylic acid and ammonium acrylate), residual carbon (styrene), and nitrogen doping (pyrrole), exhibiting a significant synergistic effect. The cationic dual-optimized dispersion of acrylic acid carboxyl groups and ammonium monomers, without interference from phosphate monomers affecting charge balance, achieves the best dispersion performance among the quaternary examples, with a slurry solid content of 57% and a milling time of 1.4 hours. The synergistic effect of styrene and pyrrole enhances the carbon layer quality, resulting in a residual carbon rate of 9.8%. Nitrogen doping reduces electron transport resistance, thus its specific capacity and rate performance are superior to all binary and ternary functional carbon sources. However, the lack of phosphate monomers means the carbon source and precursor lack coordination bonding, leading to micropores in the carbon coating layer and insufficient interfacial bonding, limiting further breakthroughs in electrochemical performance.

[0114] The functional carbon source prepared in Example 8 exhibits the best dispersion and coating properties. Methacrylic acid and ammonium acrylate synergistically regulate charge, and phosphate monomers form coordination bonds with the precursor, reducing slurry viscosity while improving dispersion stability. Therefore, with a solid content of 58% and a milling time of 1.3 hours, it ranks among the best milling efficiencies of all examples. It also has a styrene content of 50% and a residual carbon rate of 10.5%, resulting in excellent carbon layer density. However, it lacks nitrogen-containing heterocyclic monomers and has no N-doped modification, leading to high electron transport resistance and the lowest rate performance among the quaternary examples at only 82.8%. Furthermore, the absence of N-element optimization for interfacial compatibility results in a lower specific capacity than the carbon-coated lithium iron phosphate material prepared in Application Example 7.

[0115] The functional carbon source prepared in Example 9 exhibits complete functions including dispersion (acrylic acid and high-efficiency ammonium compounds), coating (phosphate compounds), and N-doping (pyridine). With a pyridine content of 40% and a high N-doping concentration, its rate performance reaches 85.2%, superior to the carbon-coated lithium iron phosphate material prepared in Example 8. The high-efficiency ammonium compounds and acrylic acid work synergistically to provide good dispersion. However, the lack of aromatic monomers and the absence of aromatic ring structures to support the residual carbon result in a residual carbon rate of only 7.6%, the lowest among all examples. The thin and easily broken carbon layer and discontinuous conductive network lead to the lowest specific capacity among quaternary functional carbon sources, and insufficient carbon layer stability, limiting further improvement in rate performance.

[0116] The functional carbon source aromatic hydrocarbon prepared in Example 10 uses vinylnaphthalene and imidazole to form a composite branch, with the two working synergistically. Vinylnaphthalene increases the residual carbon content to 11.3% (the highest among all examples), and imidazole has better N-doping efficiency than pyrrole and pyridine, thus the carbon layer has the best conductivity, and the specific capacity and rate performance are the highest among the quaternary examples. Ethyl acrylate and methacrylamide synergistically regulate dispersion, and the performance is similar to the carbon-coated lithium iron phosphate material prepared in Application Example 7. However, the lack of phosphate monomers results in weak bonding between the carbon source and the precursor. Although the carbon coating layer is dense, it is easy to detach from the particles, and the interfacial stability is insufficient, preventing further breakthroughs in electrochemical performance.

[0117] In the functional carbon source prepared in Example 11, phosphate monomers and pyridine synergistically optimize coating and conductivity, and styrene provides residual carbon, resulting in good specific capacity and rate performance. However, due to the lack of ammonium monomers, the dispersion performance relies solely on the carboxyl groups of acrylic acid. Without cation regulation of charge, the slurry viscosity is higher than that of the slurries prepared in Application Examples 7, 8, and 10, which contain ammonium monomers. Consequently, the solid content is the lowest, the milling time is the longest, and the dispersion efficiency is significantly weak, limiting the overall production performance.

[0118] The functional carbon source prepared in Example 12 contained all five monomers in a balanced ratio with no functional deficiencies. Acrylic acid and ammonium acrylate ensured dispersion performance, phosphate monomers enhanced interfacial bonding, styrene provided residual carbon, and pyrrole achieved N doping. The functions worked synergistically without any significant weaknesses. However, the chain structure consisted of independent branches, with slight charge interference between the four branches. Furthermore, the styrene content was only 25%, resulting in a lower residual carbon rate than the example containing high aromatic hydrocarbons. The N doping efficiency of pyrrole was also moderate. Therefore, while the electrochemical performance was balanced, it was not optimal.

[0119] In Example 13, the proportion of acrylic acid in the functional carbon source was increased to 40%, resulting in increased carboxyl density and enhanced main chain dispersion. Although the proportion of ammonium monomers decreased, they still helped regulate charge, thus achieving the best dispersion performance among all examples. The solid content was 60%, and the milling time was 1.1 hours. However, the excessively high proportion of acrylic acid squeezed out aromatic monomers (styrene 22%), reducing the residual carbon rate to 8.9% and resulting in insufficient carbon layer density. The proportion of phosphate monomers was only 8%, weakening the coordination effect and slightly reducing the carbon coating binding force. This led to slightly lower specific capacity and rate performance compared to the carbon-coated lithium iron phosphate material prepared in Application Example 12. Overall, the performance was biased towards dispersion optimization, with a slight sacrifice in electrochemical performance.

[0120] In the functional carbon source prepared in Example 14, imidazole was selected as the nitrogen-containing heterocyclic compound, and its proportion was increased to 25%. The N atom activity of imidazole is higher than that of pyrrole and pyridine. The N doping concentration and efficiency are both optimal, which can construct a dense N-doped conductive network, significantly reducing electron transport resistance. At the same time, it optimizes the interfacial compatibility between the carbon layer and lithium iron phosphate particles. Therefore, the specific capacity (168.7 mAh / g) and rate retention (87.5%) are the characteristics of the five-element functional carbon source of this invention. Acrylic acid and ammonium acrylate synergistically regulate charge, ensuring good dispersion performance. The solid content and sand milling time are within a reasonable range. Dihydropropylene phosphate and styrene form a composite branch. The coordination effect of the phosphate group enhances the binding force between the carbon source and the precursor. Styrene (25%) provides sufficient aromatic ring structure, increasing the residual carbon rate to 10.1%. The carbon layer is dense and firmly bonded, effectively preventing carbon layer detachment. The five monomers form a synergistic and complementary relationship with no obvious functional shortcomings. The chain structure design of composite branches and high-density imidazole branches reduces charge interference between branches, further optimizing the overall performance.

[0121] In Example 15, the functional carbon source used vinylnaphthalene as the aromatic hydrocarbon, with its proportion increased to 35%. It has a large number of aromatic rings, strong thermal stability, and a carbon residue rate of 11.8% (the highest among all examples). The carbon layer has uniform thickness and excellent density, providing a stable channel for electron transport. The ammonium monomer used is highly efficient dimethyl diallyl ammonium chloride, which synergistically regulates charge with acrylic acid and has excellent dispersion performance. The phosphate monomer forms a composite branch with pyridine, and the coordination effect and N doping synergistically optimize the interface binding and conductivity. The overall chain structure design is reasonable, with little interference between branches, and the functions of the five monomers are maximized, resulting in the best comprehensive performance.

[0122] In Example 16, the proportion of phosphate monomers in the functional carbon source was increased to 18%, the number of phosphate groups increased, and the coordination with the precursor hydroxyl groups was significantly enhanced. The carbon source and lithium iron phosphate particles were exceptionally firmly bonded, the carbon coating layer did not peel off or have pores, and the interface stability was optimal. Acrylic acid and ammonium acrylate ensured dispersion performance, imidazole achieved efficient N doping, and styrene provided basic residual carbon. However, the proportion of phosphate monomers was too high, some phosphate groups agglomerated, slightly affecting the charge balance, and crowding out the proportion of aromatic monomers. The residual carbon rate was lower than that of the high aromatic examples. Therefore, the electrochemical performance was slightly lower than that of the carbon-coated lithium iron phosphate material prepared in Application Example 15.

[0123] The functional carbon source prepared in Example 17 has a low proportion of each functional monomer, especially phosphate monomers, which account for only 5%, resulting in weak coordination and insufficient carbon coating uniformity; ammonium monomers account for 10%, with limited dispersion adjustment ability; aromatic monomers account for 30%, with moderate residual carbon rate; and pyrrole has average N doping efficiency, resulting in all performance characteristics being at the medium level of five-element functional carbon sources, without any outstanding advantages, but with stable performance, making it suitable for low-cost production scenarios where the requirements for various indicators are not high.

[0124] In summary, the functional carbon source of the present invention can effectively increase the solid content of the lithium iron phosphate precursor slurry during sand milling and shorten the sand milling time. At the same time, the carbon source has a high residual carbon rate, and the carbon-coated lithium iron phosphate obtained has excellent specific capacity and rate retention rate, with outstanding overall performance.

[0125] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited to the specific details in the above embodiments. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solution of the present invention, and these simple modifications all fall within the protection scope of the present invention.

[0126] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. In order to avoid unnecessary repetition, the present invention will not describe the various possible combinations separately.

[0127] Furthermore, various different embodiments of the present invention can be combined in any way, as long as they do not violate the spirit of the present invention, they should also be regarded as the content disclosed by the present invention.

Claims

1. A functional carbon source, characterized in that, The functional carbon source is polymerized from two or more of the following: acrylic monomers, ammonium monomers, phosphate monomers, aromatic monomers, and nitrogen-containing heterocyclic monomers. The number-average molecular weight of the functional carbon source is 5000~50000 Da.

2. The functional carbon source according to claim 1, characterized in that, The acrylic monomers are selected from one or more of acrylic acid, methacrylic acid and ethyl acrylate; The ammonium monomer is selected from one or more of ammonium acrylate, methacrylamide, and dimethyl diallyl ammonium chloride; The phosphate monomers are selected from one or more of vinyl dihydrogen phosphate, propylene dihydrogen phosphate, and vinylphosphonic acid; The aromatic monomers are selected from one or more of styrene, p-methylstyrene and vinylnaphthalene; The nitrogen-containing heterocyclic monomer is selected from one or more of pyrrole, pyridine, and imidazole.

3. The functional carbon source according to claim 1 or 2, characterized in that, In the functional carbon source, by molar percentage, acrylic monomers account for 20-45%, ammonium monomers account for 0-20%, phosphate monomers account for 0-18%, aromatic monomers account for 0-60%, and nitrogen-containing heterocyclic monomers account for 0-50%; the sum of the molar percentages of each monomer is 100%. In the functional carbon source, acrylic monomers serve as the main chain backbone and / or branched functional groups; ammonium monomers are embedded in the main chain or serve as branched monomers; phosphate monomers are grafted onto the main chain or form copolymer branches; aromatic monomers form copolymer branches or are embedded in the main chain; and nitrogen-containing heterocyclic monomers serve as branched functional monomers.

4. A method for preparing a functional carbon source as described in any one of claims 1-3, characterized in that, The preparation method includes the following steps: 1) Dissolve water-soluble monomers in water to obtain an aqueous solution; dissolve oil-soluble monomers in an organic solvent to obtain an organic solution; 2) First, heat the aqueous solution, then add dropwise a mixture of organic solution and initiator to carry out the polymerization reaction, cool, adjust the pH, evaporate and concentrate, and dry to obtain a functional carbon source; The water-soluble monomer is selected from one or more of acrylic monomers, ammonium monomers, and phosphate monomers; The oil-soluble monomers are aromatic monomers and / or nitrogen-containing heterocyclic monomers.

5. The preparation method according to claim 4, characterized in that, The acrylic monomers are selected from one or more of acrylic acid, methacrylic acid and ethyl acrylate; The ammonium monomer is selected from one or more of ammonium acrylate, methacrylamide, and dimethyl diallyl ammonium chloride; The phosphate monomers are selected from one or more of vinyl dihydrogen phosphate, propylene dihydrogen phosphate, and vinylphosphonic acid; The aromatic monomers are selected from one or more of styrene, p-methylstyrene and vinylnaphthalene; The nitrogen-containing heterocyclic monomer is selected from one or more of pyrrole, pyridine, and imidazole.

6. The preparation method according to claim 4 or 5, characterized in that, In step 1), the organic solvent is selected from one or more of ethanol, methanol, and isopropanol; The mass concentration of the aqueous solution is 20-30%; The mass concentration of the organic phase solution is 30-40%; In step 2), the heating conditions include: purging nitrogen gas into the aqueous solution for 20-40 minutes, raising the temperature to 60-80°C, and adjusting the stirring speed to 200-300 r / min; The initiator is ammonium persulfate and / or azobisisobutyronitrile; The amount of the initiator is 0.5-2% of the total monomer mass; The volume ratio of the organic phase solution to the initiator in the mixture of the organic phase solution and the initiator is 8~12:1; The polymerization reaction conditions include: adding the mixture of the organic phase solution and the initiator dropwise at a temperature of 60~80℃ and a stirring speed of 200~300r / min for 2~3h, and keeping it at that temperature for 4~6h. In step 3), the conditions for adjusting the pH include: adjusting the pH of the reaction product to 6.5-7.5 using sodium hydroxide solution, sodium bicarbonate solution, or hydrochloric acid solution; The drying method is freeze drying.

7. The application of a functional carbon source as described in any one of claims 1-3 in the synthesis of lithium iron phosphate.

8. A method for preparing carbon-coated lithium iron phosphate, characterized in that, The preparation method includes the following steps: S1. A mixed slurry is prepared by mixing lithium iron phosphate precursor, functional carbon source, conventional carbon source and dispersion medium. S2. The mixed slurry is fed into a sand mill for sand milling, and then spray-dried to obtain lithium iron phosphate precursor powder; S3. The lithium iron phosphate precursor powder is pre-calcined and sintered in sequence under inert gas protection to obtain carbon-coated lithium iron phosphate. The functional carbon source is the functional carbon source described in any one of claims 1-3.

9. The preparation method according to claim 8, characterized in that, In step S1, the dispersion medium is water and / or ethanol; In step S2, the conditions for sand milling include: the size of the zirconium beads in the sand mill is 0.4~0.8μm, the sand milling speed is 2000~2500r / min, and the sand milling time is 1~2.5h; The conditions for spray drying include: an inlet air temperature of 180~220℃ and an outlet air temperature of 80~100℃. In step S3, the pre-firing conditions include: a temperature of 300~400℃ and a time of 1~3h; The sintering conditions include: a temperature of 600~800℃ and a time of 3~8h; The inert gas is nitrogen and / or argon.

10. A carbon-coated lithium iron phosphate main material prepared by the preparation method as described in claim 8 or 9, characterized in that, The carbon-coated lithium iron phosphate main material has a 0.1C specific capacity of 162~168 mAh / g and a 5C rate retention rate of 82~89%.

Images