A composite dispersant for carbon-coated lithium iron phosphate precursor and application thereof

Abstract

This invention discloses a composite dispersant for carbon coating of lithium iron phosphate precursors and its application, comprising a main dispersant A and an auxiliary dispersant B. The main dispersant A is a terpolymer containing structural units a, b, and c; structural unit a is isopentenyl alcohol polyoxyethylene ether; structural unit b is derived from acrylic acid or its salts; and structural unit c is derived from a hydrophobic associating monomer, wherein the hydrophobic associating monomer is a C8-C18 alkyl methacrylate. The auxiliary dispersant B is an acetylenic diol compound. This invention exhibits excellent synergistic viscosity-reducing effect, superior antifoaming function, strong process adaptability, high product purity, and significantly improved production efficiency.

Description

Technical Field

[0001] This invention belongs to the field of battery materials technology, and particularly relates to a composite dispersant for carbon coating of lithium iron phosphate precursors and its application. Background Technology

[0002] Lithium iron phosphate (LFP) has become an important cathode material in the fields of power batteries and energy storage batteries due to its advantages such as high safety, long life and low cost. Its production usually adopts a wet process, which involves grinding the LFP precursor and a carbon source (such as glucose) together in an aqueous medium, spray drying and high-temperature sintering to achieve uniform carbon coating.

[0003] To improve production efficiency and reduce energy consumption, the industry urgently needs to increase the solids content of slurries. However, when the solids content exceeds 45%, the huge specific surface area of ​​submicron-sized LFP particles leads to a sharp increase in van der Waals forces between particles, easily forming a three-dimensional network agglomeration structure that traps a large amount of water, causing the slurry viscosity to soar and its flowability to deteriorate. Especially after the addition of a carbon source, sugar molecules may bridge the particles, further exacerbating the viscosity problem. High-viscosity slurries result in high energy consumption in sand milling, significant equipment wear, low grinding efficiency, and ultimately cause the spray drying tower to stick to the walls and become clogged, making continuous production impossible.

[0004] Currently, polycarboxylate-based dispersants (PCEs) are commonly used to solve slurry dispersion problems. However, in complex systems with extremely high solids content and containing carbon sources, their dispersion effectiveness is often insufficient, and high-speed sand milling easily introduces air bubbles. The addition of traditional defoamers may also bring new problems such as poor compatibility and the introduction of impurities. Therefore, developing a dedicated dispersant that can simultaneously and efficiently reduce viscosity and suppress foam, and is suitable for LFP wet coating processes, has become an urgent need in the industry. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to overcome the deficiencies and defects mentioned in the background art above, and to provide a composite dispersant for carbon coating of lithium iron phosphate precursor and its application, so as to effectively reduce viscosity and suppress foam, and is suitable for LFP wet coating process.

[0006] To solve the above-mentioned technical problems, the technical solution proposed by this invention is as follows: A composite dispersant for carbon coating of lithium iron phosphate precursors, comprising a main dispersant A and an auxiliary dispersant B; The main dispersant A is a terpolymer comprising structural unit a, structural unit b and structural unit c; structural unit a is isopentenyl polyoxyethylene ether, structural unit b is derived from acrylic acid or its salt, and structural unit c is derived from a hydrophobic associating monomer, wherein the hydrophobic associating monomer is a C8-C18 alkyl methacrylate. The auxiliary dispersant B is an acetylenic diol compound.

[0007] As a further improvement, the molar ratio of structural unit b to structural unit a is 3.0:1 to 5.0:1; the molar fraction of structural unit c in the terpolymer is 0.5% to 5.0% of the total monomer content.

[0008] As a further improvement, the hydrophobic associating monomer is selected from at least one of lauryl methacrylate and stearyl methacrylate.

[0009] As a further improvement, the acetylidene diol compound is selected from one or more of 2,4,7,9-tetramethyl-5-decyn-4,7-diol or its ethoxylated derivatives.

[0010] As a further improvement, the mass ratio of the primary dispersant A to the auxiliary dispersant B is 5:1 to 20:1.

[0011] As a further improvement, the synthesis method of the main dispersant A is as follows: S1. Mix isopentenyl alcohol polyoxyethylene ether monomer, hydrophobic associating monomer, reactive emulsifier and water, and perform shear pre-emulsification to obtain microemulsion; S2. Under an inert atmosphere, heat the microemulsion obtained in step S1 to 70-80°C, and then add an aqueous solution of acrylic acid and an aqueous solution containing an initiator and a chain transfer agent dropwise. S3. After the addition is complete, maintain the temperature at 70-80℃ for the reaction. S4. Cool the reaction system and add an organic amine neutralizing agent to neutralize it, thereby obtaining an aqueous solution of the main dispersant A.

[0012] The present invention also provides the application of the composite dispersant in the preparation of lithium iron phosphate cathode material precursor slurry, wherein the total amount of the composite dispersant added is 0.1% to 1.0% of the mass of iron phosphate.

[0013] As a further improvement, the solid content of the precursor slurry is not less than 45%.

[0014] As a further improvement, the preparation process of the lithium iron phosphate cathode material precursor slurry includes: adding the carbon source glucose and the composite dispersant to a mixture of iron phosphate and lithium carbonate, adding water to adjust the solid content, and then performing sand milling.

[0015] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) Excellent synergistic viscosity reduction effect: As a highly efficient dynamic wetting agent, acetylsadiol compounds can quickly penetrate into the interior of LFP particle agglomerates, causing them to initially depolymerize; the polycarboxylic acid polymers then provide a strong steric hindrance effect, achieving deep dispersion. The synergistic effect of the two can significantly reduce the viscosity of high solids content slurries.

[0016] (2) It also has excellent defoaming function: Alkyne diol compounds have a high-efficiency defoaming effect, which inhibits the generation of bubbles during the sand milling process from the source, avoiding problems such as poor compatibility, shrinkage pores, and introduction of impurities that may be caused by adding additional defoamers.

[0017] (3) Strong process adaptability: The dispersant of this invention has good compatibility with carbon sources such as glucose, and is perfectly adapted to the LFP wet coating process, ensuring the long-term stability of the slurry.

[0018] (4) High product purity: The main dispersant uses organic amines for neutralization, which avoids the introduction of alkali metal ions such as sodium and potassium. There are no residues after sintering, which ensures the electrochemical performance of the final LFP material.

[0019] (5) Production efficiency is greatly improved: The low viscosity and low foaming properties of the slurry greatly improve the efficiency of sand milling and the smoothness of spray drying, thereby improving production efficiency and product consistency. Attached Figure Description

[0020] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0021] Figure 1 The image shows an electron microscope (EM) image of the cathode material obtained in Comparative Example 1 without the use of a composite dispersant. Figure 2 The image shows an electron microscope (EM) image of the cathode material obtained by adding 0.3% composite dispersant in Example 2. Figure 3 This is the infrared spectrum of the main dispersant A in Example 1. Detailed Implementation

[0022] To facilitate understanding of the present invention, the present invention will be described more fully and in detail below with reference to the accompanying drawings and preferred embodiments, but the scope of protection of the present invention is not limited to the following specific embodiments.

[0023] Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the scope of the invention.

[0024] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this invention can be purchased from the market or prepared by existing methods.

[0025] In some specific embodiments, the composite dispersant for carbon coating of lithium iron phosphate precursors of the present invention is composed of a main dispersant A and an auxiliary dispersant B.

[0026] Wherein, the main dispersant A is a terpolymer comprising structural unit a, structural unit b and structural unit c; structural unit a is isopentenyl polyoxyethylene ether (e.g. TPEG-2400); structural unit b is derived from acrylic acid or its salt; structural unit c is derived from a hydrophobic associating monomer, wherein the hydrophobic associating monomer is a C8-C18 alkyl methacrylate.

[0027] The auxiliary dispersant B is an acetylenic diol compound.

[0028] Preferably, the molar fraction of the structural unit c in the terpolymer is 0.5% to 5.0% of the total monomer content, more preferably 1.0% to 3.0%.

[0029] Preferably, the molar ratio of structural unit b to structural unit a is 3.0:1 to 5.0:1.

[0030] Preferably, the hydrophobic associating monomer is selected from at least one of lauryl methacrylate and stearyl methacrylate.

[0031] Preferably, the acetylidene diol compound is selected from one or more of 2,4,7,9-tetramethyl-5-decyn-4,7-diol or its ethoxylated derivatives.

[0032] Preferably, the mass ratio of the main dispersant A to the auxiliary dispersant B is 5:1 to 20:1. The main dispersant A and the auxiliary dispersant B are stirred and mixed evenly to obtain the composite dispersant of the present invention.

[0033] In the main dispersant A, multiple polymer molecules are interconnected through hydrophobic association points, forming a pervasive, dynamically reversible weak gel network within the slurry. This significantly imparts "thixotropic" properties to the slurry: the network forms upon standing (high viscosity prevents sedimentation), and the network breaks down upon shearing (low viscosity facilitates processing).

[0034] The rigid triple bond at the center of the acetylinyl glycol molecule and the multiple adjacent methyl (-CH3) groups form a compact, rigid hydrophobic framework. This structural feature endows it with low foaming properties and excellent defoaming properties: traditional surfactants (such as alkylphenol polyoxyethylene ethers) have long, flexible hydrophobic chains that easily form stable, dense films at the gas-liquid interface, thus stabilizing foam. However, the rigid hydrophobic framework of acetylinyl glycol makes it difficult for it to form a stable liquid film through close packing, thus inherently resulting in low foaming. It can also penetrate and disrupt existing foam films, possessing both wetting and defoaming functions. This is crucial in the high-speed stirring preparation of slurries, preventing air bubble entrainment that leads to uneven coating.

[0035] The acetylenic diol molecule has polar hydrophilic hydroxyl groups at both ends. Due to the compact nature of the molecule, the hydrophilicity of these hydroxyl groups is relatively mild. This structural feature allows for dynamic wetting and rapid migration: the small molecular weight of acetylenic diol and its amphiphilic structure (one end hydrophobic, the other hydrophilic) enable it to migrate rapidly from the aqueous phase to the interface (solid-liquid, gas-liquid interface). It can rapidly reduce the surface tension and solid-liquid interfacial tension of the slurry, making it easier for the slurry to penetrate into the gaps of the tightly aggregated carbon nanoparticles, thus "opening channels" for the subsequent adsorption and dispersion of the polymeric dispersant (A). In addition, the hydroxyl groups can form weak hydrogen bonds with trace amounts of oxygen-containing functional groups on the surface of carbon materials or certain segments of the main dispersant A, providing certain adsorption anchoring sites.

[0036] This invention employs a composite system of primary dispersant A and auxiliary dispersant B, which function synergistically: First, in the initial stage of stirring, the small-molecule acetylacetic diol, with its ability to migrate rapidly and efficiently reduce interfacial tension, first wets and penetrates into the interior of the carbon nanoparticle aggregates, breaking their original hydrophobic aggregate state and causing them to initially depolymerize.

[0037] Subsequently, the high molecular weight polycarboxylic acid dispersant is strongly adsorbed onto the surface of the wetted and depolymerized carbon particles through multiple anchoring groups (carboxyl-COOH) on its main chain. Its long hydrophilic side chains (TPEG chains) extend fully in water, forming a strong steric hindrance layer that prevents the particles from agglomerating again, thus providing long-term thermodynamic stability.

[0038] The construction of hydrophobic associative networks differs significantly from that of ordinary polycarboxylate. Long-chain alkyl groups (structural unit c) sparsely distributed along the polymer chain associate with each other in water due to hydrophobic interactions. This association occurs not only at different sites within the same molecular chain but also between different polymer molecules adsorbed on the surfaces of different particles, thus forming a dynamically reversible physical cross-linked network spanning the entire system within the slurry.

[0039] Among them, acetylinyl glycol addresses the shortcomings of polycarboxylate polymers: when used alone, polycarboxylate polymers may be sensitive to microbubbles and have insufficient initial wetting speed. The low-foaming / defoaming properties and rapid wetting of acetylinyl glycol perfectly compensate for these deficiencies.

[0040] Polycarboxylate polymers enhance overall stability: When used alone, acetylacetonate diols have limited stabilizing effects due to their weak molecular adsorption. Polycarboxylate polymers provide long-lasting and powerful stabilizing effects.

[0041] The combined effect of these two factors can reduce the viscosity of slurries with high solids and carbon content, while maintaining better fluidity and processability, which is crucial for subsequent processes such as spray drying.

[0042] In some embodiments, the method for synthesizing the primary dispersant A is as follows: S1. Pre-emulsification: The isopentenyl alcohol polyoxyethylene ether (e.g., TPEG-2400) monomer, hydrophobic associating monomer, reactive emulsifier and a portion of deionized water are mixed and subjected to high-speed shear pre-emulsification to form a stable microemulsion. S2, Copolymerization reaction: Under an inert atmosphere, the microemulsion obtained in step S1 is heated to 70-80°C, and then an aqueous solution of acrylic acid and an aqueous solution containing an initiator and a chain transfer agent are added dropwise to the system simultaneously, with the dropwise addition time controlled to be 2-4 hours. S3. Incubation and ripening: After the addition is complete, keep the reaction at 70-80℃ for 1-3 hours. S4. Post-treatment: Cool the reaction system to below 40°C, add an organic amine neutralizer for neutralization, adjust the pH value to 6.0-7.0, and obtain an aqueous solution of the main dispersant A with a solid content of about 40% and a viscosity of about 300~1200 mPa·s.

[0043] Preferably, the reactive emulsifier is selected from at least one of: 2-acrylamide-2-methylpropanesulfonate ammonium salt, methacryloyloxyethyl sulfobetaine, and allyloxyhydroxypropyl sulfonate ammonium salt.

[0044] Preferably, the organic amine neutralizing agent is selected from at least one of: monoethanolamine, diethanolamine, triethanolamine, aminomethylpropanol, 2-amino-2-methyl-1-propanol, and N,N-dimethylethanolamine.

[0045] Preferably, the initiator is a water-soluble azo initiator or ammonium persulfate, and the chain transfer agent is mercaptopropionic acid or mercaptoacetic acid.

[0046] The present invention also provides the application of the aforementioned composite dispersant in the preparation of lithium iron phosphate cathode material precursor slurry.

[0047] Preferably, the total amount of the composite dispersant added is 0.1% to 1.0% of the mass of ferric phosphate.

[0048] Preferably, the solid content of the slurry is not less than 45%. Wherein, solid content = (total mass of iron phosphate + lithium carbonate + glucose in the slurry) / total mass of the slurry.

[0049] Preferably, the preparation process of the lithium iron phosphate cathode material includes: precursor slurry preparation, spray granulation, and calcination.

[0050] In preparing the precursor slurry, iron phosphate and lithium carbonate are first added at an iron:lithium molar ratio of 1:0.9~1.05. Then, 8%~12% of the iron phosphate mass of glucose and a dispersant are added. Finally, water is added to adjust the solid content to 45~55%. The mixture is then milled in a sand mill at 1500 r / min to control the particle size D50 at around 500 nm, thus obtaining the lithium iron phosphate cathode material precursor slurry.

[0051] During spray granulation, the inlet temperature is controlled at 210~240℃, the outlet temperature is controlled at around 100℃, and the powder moisture content is controlled at ≥98%.

[0052] During the firing process, the material is first calcined at a low temperature of about 250~350℃ for 1~5 hours in an inert atmosphere, and then heated to a high temperature of about 650~800℃ and held for 6~10 hours to obtain lithium iron phosphate cathode material.

[0053] Example 1 (Synthesis of Main Dispersant A) In a 1000 mL four-necked flask equipped with a stirrer, condenser, thermometer, and nitrogen inlet tube, add the following components: Isopentenyl alcohol polyoxyethylene ether (TPEG-2400): 120.0g Lauryl methacrylate (LMA): 1.5g (1.97% of the total monomer moles) 2-Acrylamide-2-methylpropanesulfonate ammonium salt (AMPS-NH4, 50% aqueous solution): 3.6 g (1.8 g on solids) Deionized water: 120.0g Turn on the high-speed homogenizer and pre-emulsify at 3000 rpm for 40 minutes to obtain a uniform and stable milky white microemulsion.

[0054] Nitrogen gas was introduced for 30 minutes to replace the air, and the temperature was raised to 75°C.

[0055] Prepare the following solutions respectively: Solution C: 17.5g of acrylic acid (AA) dissolved in 25g of deionized water (in this example, the molar ratio of acrylic acid to isopentenyl alcohol polyoxyethylene ether n(AA):n(TPEG-2400) = 4.86:1). Solution D: 0.8 g of azobisisobutyramidine hydrochloride (V-50) and 0.5 g of mercaptopropionic acid dissolved in 35 g of deionized water.

[0056] Once the temperature stabilizes at 75℃, begin the simultaneous dropwise addition of solutions C and D, controlling the dropping rate to complete the addition within 3.5 hours. After the addition is complete, maintain the reaction at 75℃ for 2 hours.

[0057] After the reaction was completed, the mixture was cooled to 35°C, and triethanolamine was slowly added dropwise while stirring to adjust the pH to 6.8. A pale yellow, transparent, viscous liquid with a solid content of about 40% and a viscosity of about 750 mPa·s was obtained, which is the hydrophobic associative polycarboxylic acid dispersant (main dispersant A).

[0058] The reaction equation for synthesizing the main dispersant A in this embodiment is: CH2=C(CH3)CH2O-(CH2CH2O) 55 -H+CH2=CH-COOH+CH2=C(CH3)-COO-C 12 H 25 → HO-(CH2CH2O) 55 -CH2-C(CH3)2-CH2-co-CH2-CH(COOH)-co-CH2-C(CH3)(COOC 12 H 25 ).

[0059] Characterization of main dispersant A: The infrared spectrum of main dispersant A is shown below. Figure 3 As shown.

[0060] Example 2 The main dispersant A solution prepared in Example 1 and 2,4,7,9-tetramethyl-5-decyn-4,7-diol (auxiliary dispersant B) were added at a solid-to-solid mass ratio of 10:1. The mixture was mechanically stirred at 200 rpm for 30 minutes at room temperature until homogeneous, thus obtaining a composite dispersant. In the preparation of lithium iron phosphate cathode material precursor slurry, the addition amounts were 0.1%, 0.3%, and 0.5% of the mass of iron phosphate, respectively.

[0061] Example 3 The primary dispersant A solution prepared in Example 1 and 2,4,7,9-tetramethyl-5-decyn-4,7-diol (auxiliary dispersant B) were mixed in a solid-to-solid ratio of 5:1. The mixture was mechanically stirred at 200 rpm for 30 minutes at room temperature until homogeneous, yielding a composite dispersant. When preparing the lithium iron phosphate cathode material precursor slurry, the amount added was 0.3% of the mass of iron phosphate.

[0062] Example 4 The primary dispersant A solution prepared in Example 1 and 2,4,7,9-tetramethyl-5-decyn-4,7-diol (auxiliary dispersant B) were mixed in a solid-to-solid ratio of 15:1. The mixture was mechanically stirred at 200 rpm for 30 minutes at room temperature until homogeneous, yielding a composite dispersant. When preparing the lithium iron phosphate cathode material precursor slurry, the amount added was 0.3% of the mass of iron phosphate.

[0063] Example 5 The primary dispersant A solution prepared in Example 1 and 2,4,7,9-tetramethyl-5-decyn-4,7-diol (auxiliary dispersant B) were mixed in a solid-to-solid ratio of 20:1. The mixture was mechanically stirred at 200 rpm for 30 minutes at room temperature until homogeneous, yielding a composite dispersant. When preparing the lithium iron phosphate cathode material precursor slurry, the amount added was 0.3% of the mass of iron phosphate.

[0064] Comparative Example 1 No dispersant is added.

[0065] Comparative Example 2 Only the main dispersant A prepared in Example 1 was used, without adding acetylacetonate diol. When preparing the lithium iron phosphate cathode material precursor slurry, the amount added was 0.3% of the mass of iron phosphate.

[0066] Comparative Example 3 Only auxiliary dispersant B (2,4,7,9-tetramethyl-5-decyn-4,7-diol) was used, without adding primary dispersant A. In preparing the lithium iron phosphate cathode material precursor slurry, the amount added was 0.3% of the mass of iron phosphate.

[0067] Application effect verification experiment Precursor slurry preparation: Take 100g of ferric phosphate, 24.97g of lithium carbonate, and 10g of glucose. Finally, add water and the dispersant from the example / comparative example. Mill the mixture in a sand mill at 1500r / min, controlling the particle size D50 to be around 500nm, to prepare a precursor slurry with a solid content of 50%. (When the dispersant content exceeds 0.3%, appropriately reduce the amount of glucose to ensure consistent total coated carbon content.) Preparation of lithium iron phosphate cathode material: The precursor slurry was spray-granulated, with the inlet temperature controlled at around 220℃ and the outlet temperature controlled at around 100℃, and the powder moisture content controlled at ≥98%. Then, it was calcined in an inert atmosphere, first at a low temperature of around 300℃ for 2 hours, and then heated to a high temperature of around 700℃ and held for 8 hours to obtain the lithium iron phosphate cathode material.

[0068] Figure 1 and Figure 2 The comparison shows that adding a composite dispersant results in a better dispersion effect.

[0069] Performance testing: Viscosity: The viscosity of the slurry at 60 rpm on rotor No. 2 was measured using a Brookfield viscometer, and the static flowability of the slurry was observed.

[0070] Powder resistance: using a powder resistance meter Battery Performance: The obtained lithium iron phosphate cathode material, conductive carbon black (Super P), and polyvinylidene fluoride (PVDF) were mixed at a mass ratio of 90:5:5 to form a slurry, which was then coated onto carbon-coated aluminum foil to prepare a cathode sheet. Using a lithium metal sheet as the counter electrode, ethylene carbonate (EC), dimethyl carbonate (DMC), and diethyl carbonate (DEC) were mixed at a volume ratio of 1:1:1 in an argon-protected glove box to prepare the required electrolyte. CR2032 coin cells were then assembled in the same glove box. Charge-discharge tests were conducted at room temperature.

[0071] Rate performance: The battery discharge capacity was tested at 0.2C, 1C, 2C, and 5C rates.

[0072] Cyclic performance: The capacity retention rate of the battery after 100 cycles at 1C rate is tested.

[0073] Settling stability index: The solid content difference method is used for testing. A uniform slurry after sand milling is taken with a 100ml graduated cylinder and the initial solid content C1 is tested. After standing at 25℃ for 72h, the upper layer of slurry is taken and the solid content C2 is tested (the test is repeated three times). Settling stability index = (C1-C2) / C1.

[0074] Performance data for the embodiments and comparative examples are shown in Table 1: Table 1

[0075] It can be seen that the optimal addition amount of the composite dispersant is 0.3-0.5% of the mass of ferric phosphate. The optimal solid-to-solid mass ratio of the main dispersant A solution to the auxiliary dispersant B is 10:1. In Comparative Examples 2 and 3, whether using only the main dispersant A or only the auxiliary dispersant B, the viscosity was significantly higher than that of Example 2 (0.3% of the same addition amount), and the electrical properties and stability were significantly lower than those of Example 2.

[0076] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention in any way. Therefore, any simple modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention should fall within the protection scope of the present invention.

Claims

1. A composite dispersant for carbon-coated lithium iron phosphate precursor, characterized in that, It consists of main dispersant A and auxiliary dispersant B; The main dispersant A is a terpolymer comprising structural unit a, structural unit b and structural unit c; structural unit a is isopentenyl polyoxyethylene ether, structural unit b is derived from acrylic acid or its salt, and structural unit c is derived from a hydrophobic associating monomer, wherein the hydrophobic associating monomer is a C8-C18 alkyl methacrylate. The auxiliary dispersant B is an acetylenic diol compound.

2. The carbon-coated composite dispersant for lithium iron phosphate precursor according to claim 1, characterized in that, The molar ratio of structural unit b to structural unit a is 3.0:1 to 5.0:1; the molar fraction of structural unit c in the terpolymer is 0.5% to 5.0% of the total monomer content.

3. The carbon-coated composite dispersant for lithium iron phosphate precursor according to claim 1, characterized in that, The hydrophobic associating monomer is selected from at least one of lauryl methacrylate and stearyl methacrylate.

4. The carbon-coated composite dispersant for lithium iron phosphate precursor according to claim 1, characterized by, The acetylenic diol compound is selected from one or more of 2,4,7,9-tetramethyl-5-decyn-4,7-diol or its ethoxylated derivatives.

5. The carbon-coated composite dispersant for lithium iron phosphate precursor according to claim 1, characterized by, The mass ratio of the primary dispersant A to the auxiliary dispersant B is 5:1 to 20:

1.

6. The carbon-coated composite dispersant for lithium iron phosphate precursor according to claim 1, characterized by, The synthesis method of the main dispersant A is as follows: S1. Mix isopentenyl alcohol polyoxyethylene ether monomer, hydrophobic associating monomer, reactive emulsifier and water, and perform shear pre-emulsification to obtain microemulsion; S2. Under an inert atmosphere, heat the microemulsion obtained in step S1 to 70-80°C, and then add an aqueous solution of acrylic acid and an aqueous solution containing an initiator and a chain transfer agent dropwise. S3. After the addition is complete, maintain the temperature at 70-80℃ for the reaction. S4. Cool the reaction system and add an organic amine neutralizing agent to neutralize it, thereby obtaining an aqueous solution of the main dispersant A.

7. Use of the composite dispersant according to any one of claims 1-6 in the preparation of a slurry of a lithium iron phosphate cathode material precursor, characterized in that, The total amount of the composite dispersant added is 0.1% to 1.0% of the mass of ferric phosphate.

8. Use according to claim 7, characterized in that, The solid content of the precursor slurry is not less than 45%.

9. Use according to claim 7, characterized in that, The preparation process of the lithium iron phosphate cathode material precursor slurry includes: adding the carbon source glucose and the composite dispersant to a mixture of iron phosphate and lithium carbonate, adding water to adjust the solid content, and then performing sand milling.

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