Compound lithium iron phosphate dispersant, preparation method and application thereof, and lithium iron phosphate positive electrode slurry

Abstract

The application relates to the technical field of lithium ion battery positive electrode materials, in particular to a compounded lithium iron phosphate dispersant as well as a preparation method and application thereof and a lithium iron phosphate positive electrode slurry. The compounded lithium iron phosphate dispersant forms a ternary synergistic system through accurate compounding of core components, realizes the synergistic effect of strong anchoring, stable electrostatic repulsion and excellent interface compatibility, is suitable for different types of lithium iron phosphate materials, and can prepare a high-solid-content and low-viscosity lithium iron phosphate positive electrode slurry.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery cathode material technology, specifically to a compound lithium iron phosphate dispersant, its preparation method and application, and lithium iron phosphate cathode slurry. Background Technology

[0002] Lithium iron phosphate (LFP) batteries are widely used in new energy fields such as power batteries and energy storage batteries due to their advantages of high safety, long cycle life, and low cost. The preparation of LFP cathode sheets is one of the core processes in lithium battery production. The dispersion and mixing quality of the cathode slurry directly determines the coating uniformity and compaction density of the electrode sheet, which in turn has a critical impact on the energy density, cycle stability, and reliability of the lithium battery.

[0003] The preparation of positive electrode slurry requires the uniform mixing of LFP active material, conductive agent, binder, dispersant, and solvent. The dispersant, as a core auxiliary agent for regulating the dispersion stability of the slurry, is of paramount importance. Currently, existing LFP dispersants still suffer from several technical challenges in practical applications: First, insufficient anchoring effect; traditional dispersants have weak binding forces with metal ions on the LFP surface, easily leading to dispersant desorption and particle agglomeration during slurry storage or high-shear processing, resulting in significant slurry viscosity rebound and severely affecting the stability of the coating process. Second, unstable electrostatic repulsion effect; some dispersants have excessively strong electrostatic forces, easily causing electrostatic adsorption conflicts with the binder, leading to slurry flocculation; while insufficient electrostatic forces cannot effectively inhibit particle agglomeration. Third, poor interfacial compatibility; the dispersant and slurry... The insufficient compatibility of solvents, binders, and carbon layers on the LFP surface in the material can easily lead to a decrease in electrode bonding strength, discontinuity in the conductive network, and affect the electrochemical performance of the battery. Fourth, the compatibility is narrow. A single dispersant is difficult to adapt to LFP materials with different particle sizes, different carbon contents, and elements such as Mg and Mn. Frequent adjustments to process parameters are required during production, which increases production costs and reduces production efficiency. Fifth, it is difficult to prepare high-solids slurries. When the solid content of the slurry exceeds 60%, traditional dispersants will cause the slurry viscosity to increase sharply, which cannot meet the production requirements of industrial high-efficiency coating.

[0004] In response to the aforementioned technical problems of existing LFP dispersants, there is an urgent need to develop a new type of dispersant that combines strong anchoring, stable electrostatics, excellent compatibility, and adaptability to the preparation of high-solids-content slurries. Through scientific component compounding, a multi-dimensional synergistic effect can be achieved, thus solving the application bottleneck of existing dispersing technologies. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of existing lithium iron phosphate dispersants, such as insufficient anchoring effect, unstable electrostatic repulsion, poor interfacial compatibility, narrow adaptability, and difficulty in preparing high-solids-content slurries. This invention provides a compound lithium iron phosphate dispersant that forms a ternary synergistic system through the precise compounding of core components, achieving a synergistic effect of strong anchoring, stable electrostatic repulsion, and excellent interfacial compatibility. It is adaptable to different types of lithium iron phosphate materials and can prepare high-solids-content, low-viscosity lithium iron phosphate cathode slurries.

[0006] To achieve the above objectives, in a first aspect, the present invention provides a compound lithium iron phosphate dispersant, wherein the compound lithium iron phosphate dispersant is composed of a strong anchoring component B, an electrostatic repulsion component C, and an interfacial compatibility component D; wherein... The strongly anchoring component B is a high molecular weight polymer with oxazolidinone and / or hydrazide groups, with a number average molecular weight of 1000~8000 g / mol. The electrostatic repulsion component C is a high molecular weight polymer with sulfonamide groups and / or betaine-type sulfonyl groups, with a number average molecular weight of 800~6000 g / mol; The interface compatibility component D is a compound and / or polymer having sulfoxide groups and / or urea formate groups, with a number average molecular weight of 500~5000 g / mol.

[0007] Preferably, the mass ratio of the strong anchoring component B, the electrostatic repulsion component C, and the interfacial compatibility component D in the compound lithium iron phosphate dispersant is 1:0.5~1.5:0.3~1.

[0008] Preferably, the grafting rate of oxazolidinone and / or hydrazide groups in the strongly anchoring component B is ≥90%.

[0009] Preferably, the strongly anchoring component B is selected from one or more of oxazolidinone acrylate homopolymer, hydrazide methacrylate-styrene copolymer, and oxazolidinone modified polyether.

[0010] Preferably, the zeta potential of the electrostatic repulsion component C is 28~35mV.

[0011] Preferably, the electrostatic repulsion component C is selected from one or more of sulfonamide-based vinyl ether homopolymers, betaine-type sulfoacrylamide copolymers, and sulfonamide-modified polyesters.

[0012] Preferably, the interfacial compatibility component D is selected from one or more of sulfoxide ethyl ether, sulfoxide propyl ether, and urea-formaldehyde polyether.

[0013] Preferably, the compound lithium iron phosphate dispersant further contains a solvent selected from one or more of N-methylpyrrolidone, deionized water, and dimethyl sulfoxide.

[0014] Preferably, the solvent accounts for 80-90% of the total mass of the compound lithium iron phosphate dispersant.

[0015] Secondly, the present invention provides a method for preparing a compound lithium iron phosphate dispersant as described herein, the preparation method comprising: 1) Mix the strong anchoring component B, the electrostatic repulsion component C, and the interfacial compatibility component D to obtain a mixture; Optionally, 2) add solvent to the mixture obtained in step 1), and stir at 300-600 rpm for 30-60 min at a temperature of 25-60℃ to obtain a premixed system; 3) Stir the mixture from step 1) or the premixed system from step 2) at a temperature of 40~70℃ and a speed of 300~600rpm for 60~120min, and then cool to obtain the compound lithium iron phosphate dispersant.

[0016] Preferably, in step 1), the mass ratio of the strong anchoring component B, the electrostatic repulsion component C, and the interfacial compatibility component D in the compound lithium iron phosphate dispersant is 1:0.5~1.5:0.3~1.0.

[0017] Preferably, the grafting rate of oxazolidinone and / or hydrazide groups in the strongly anchoring component B is ≥90%.

[0018] Preferably, the strongly anchoring component B is selected from one or more of oxazolidinone acrylate homopolymer, hydrazide methacrylate-styrene copolymer, and oxazolidinone modified polyether.

[0019] Preferably, the zeta potential of the electrostatic repulsion component C is 28~35mV.

[0020] Preferably, the electrostatic repulsion component C is selected from one or more of sulfonamide-based vinyl ether homopolymers, betaine-type sulfoacrylamide copolymers, and sulfonamide-modified polyesters.

[0021] Preferably, the interfacial compatibility component D is selected from one or more of sulfoxide ethyl ether, sulfoxide propyl ether, and urea-formaldehyde polyether.

[0022] Preferably, in step 2), the solvent is selected from one or more of N-methylpyrrolidone, deionized water, and dimethyl sulfoxide.

[0023] Preferably, the solvent accounts for 80-90% of the total mass of the dispersant.

[0024] Thirdly, the present invention provides an application of the compound lithium iron phosphate dispersant as described in the present invention in the preparation of lithium iron phosphate cathode slurry.

[0025] Fourthly, the present invention provides a lithium iron phosphate cathode slurry, wherein the lithium iron phosphate cathode slurry is composed of the following components by mass: 57-67 parts of lithium iron phosphate base material, 1-8 parts of conductive agent, 1-5 parts of binder, 0.06-2 parts of dispersant, and 30-40 parts of slurry solvent. The dispersant is a compound lithium iron phosphate dispersant as described in this invention. The lithium iron phosphate base material is selected from one or more of lithium iron phosphate, Mg-doped lithium iron phosphate, manganese iron phosphate, and carbon-coated lithium iron phosphate.

[0026] Preferably, the conductive agent is conductive carbon black and / or carbon nanotubes; The adhesive is selected from one or more of polyvinylidene fluoride, carboxymethyl hydroxyethyl cellulose, and polyvinyl alcohol.

[0027] Preferably, the solvent for the slurry is selected from one or more of N-methylpyrrolidone, deionized water, and dimethyl sulfoxide.

[0028] Preferably, the lithium iron phosphate cathode slurry has a solid content of ≥60% and a viscosity of ≤10000 mPa·s.

[0029] In the above technical solution, the compound lithium iron phosphate dispersant of the present invention constructs a ternary synergistic system with strong anchoring, stable electrostatics, and excellent interface, where each core component has complementary functions and synergistic effects. The oxazolidinone group of the strong anchoring component B binds to the Fe atoms on the lithium iron phosphate surface through N and O atoms. 2+ A six-membered coordination ring is formed, with the hydrazide group interacting with Fe via -NHNH2. 2+ A stable chelated structure is formed, with a grafting rate of ≥90%, ensuring an adsorption strength that is more than 30% higher than that of traditional dispersants, effectively avoiding particle agglomeration caused by dispersant desorption; the electrostatic repulsion component C provides a mild and stable electrostatic repulsion force of 28~35mV, which not only inhibits secondary particle agglomeration but also does not generate electrostatic conflict with the binder, making it suitable for the preparation of high solids content slurries; the sulfoxide group of the interfacial compatibility component D is a moderately polar functional group, which is the "optimal polar bridge" at the three-phase interface of the slurry, and the urea carbamate group contains multiple hydrogen bond sites. Both can effectively reduce the interfacial tension of the slurry, optimize the interfacial compatibility between the dispersant and the solvent, binder, and carbon layer on the surface of lithium iron phosphate, and reduce the risk of phase separation.

[0030] Furthermore, each core component of the dispersant of the present invention has a precisely defined range of number-average molecular weight and mass ratio to ensure the optimal solubility, spreadability and synergistic effect of the molecular chains, and to avoid problems such as molecular chain entanglement due to excessively high molecular weight or insufficient functional sites due to excessively low molecular weight. The mass ratio is the optimal range for the synergistic effect of each component. In particular, the high solids content matching ratio of 1:1.2:0.8 can significantly reduce the viscosity of the slurry.

[0031] Meanwhile, the dispersant of this invention has wide applicability and can be directly applied to various lithium iron phosphate base materials such as lithium iron phosphate, Mg-doped lithium iron phosphate, manganese iron phosphate, lithium iron phosphate with carbon content of 1~5% and lithium iron phosphate with particle size of 0.55μm. There is no need to adjust the dispersant formulation or slurry preparation process for different base materials, which reduces process debugging time, improves production efficiency and reduces production costs.

[0032] Furthermore, the dispersant of this invention can be selected as a solvent-containing or solvent-free system according to actual production needs. The solid content of the solvent-containing system is 10-20%, which facilitates precise control of the effective addition amount of dispersant in the slurry and adapts to different slurry preparation processes. The solvent-free system is in solid powder form, which is convenient for storage and transportation.

[0033] Furthermore, the preparation method of the dispersant of the present invention is simple and can be achieved by stepwise temperature control and stirring. It does not require complex chemical reactions or special production equipment. The operation of the sealed container can effectively prevent solvent evaporation and the introduction of impurities. The preparation process is easy to control and has good repeatability. It can be directly integrated into the existing industrial production process of lithium-ion battery cathode slurry and is easy to promote and apply on a large scale.

[0034] Furthermore, the lithium iron phosphate cathode slurry prepared using the dispersant of this invention can achieve a solid content of 60-68% and a viscosity of ≤10000 mPa·s. The viscosity rebound rate of the slurry is significantly reduced, and the stability is good. The slurry preparation process is fully compatible with existing industrial processes, requiring no modification to production equipment. The prepared slurry has good coating uniformity, which can improve the compaction density and bonding strength of the electrode sheet, thereby improving the electrochemical performance of lithium batteries such as energy density and cycle stability.

[0035] Other features and advantages of the present invention will be described in detail in the following detailed description section. Attached Figure Description

[0036] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used together with the following detailed description to explain the invention, but do not constitute a limitation thereof. In the drawings: Figure 1 The infrared spectrum of the compound lithium iron phosphate dispersant prepared in Example 1 of this invention; Figure 2 The infrared spectrum of the compound lithium iron phosphate dispersant prepared in Example 2 of this invention; Figure 3 The infrared spectrum of the compound lithium iron phosphate dispersant prepared in Example 3 of this invention; Figure 4 The infrared spectrum of the compound lithium iron phosphate dispersant prepared in Example 4 of this invention; Figure 5The infrared spectrum of the compound lithium iron phosphate dispersant prepared in Example 5 of this invention; Figure 6 The infrared spectrum of the compound lithium iron phosphate dispersant prepared in Example 6 of this invention. Detailed Implementation

[0037] 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.

[0038] 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.

[0039] In a first aspect, the present invention provides a compound lithium iron phosphate dispersant, wherein the compound lithium iron phosphate dispersant is composed of a strong anchoring component B, an electrostatic repulsion component C, and an interfacial compatibility component D; wherein... The strongly anchoring component B is a polymer with oxazolidinone (-C3H5NO2, as shown in Formula 1) and / or hydrazide (-CONHNH2, as shown in Formula 2) groups, with a number average molecular weight of 1000~8000 g / mol; the grafting rate of oxazolidinone and / or hydrazide groups in the strongly anchoring component B is ≥90%. The strongly anchoring component B can bind to Fe on the LFP surface. 2+ Li + This forms a stable coordination / chelation structure, enhancing the adsorption strength of the dispersant on the LFP surface and preventing agglomeration caused by desorption. The strongly anchoring component B is selected from one or more of oxazolidinone acrylate homopolymers, hydrazide-methyl methacrylate-styrene copolymers, and oxazolidinone-modified polyethers.

[0040] For example, the strongly anchoring component B is an oxazolidinone acrylate copolymer (repeating unit as shown in Formula 3), whose chemical structure is a linear homopolymer obtained by free radical polymerization of 2-(2-oxo-1,3-oxazolidinone-3-yl)ethyl acrylate as monomer, with a degree of polymerization q of 16~27, corresponding to a number average molecular weight of 3000~5000 g / mol, and the core anchoring functional group is 2-oxo-1,3-oxazolidinone.

[0041] The strongly anchoring component B is an acylhydrazide methacrylate-styrene copolymer (repeating unit as shown in Formula 4). This copolymer is prepared by free radical solution copolymerization using 2-acetylhydrazide methacrylate and styrene as comonomers. The molar ratio of acylhydrazide methacrylate to styrene is m:n=3:1~5:1, preferably 4:1; the total degree of polymerization is q=m+n=35~45, corresponding to a number average molecular weight of 4000~5000g / mol; the core anchoring functional group is acylhydrazide (-CONHNH2), which can form a stable chelate structure with metal ions on the LFP surface, and the styrene segment improves the interfacial compatibility with carbon-coated LFP.

[0042] The electrostatic repulsion component C is a high molecular weight polymer with sulfonamide groups and / or betaine-type sulfonyl groups, with a number average molecular weight of 800~6000 g / mol; the zeta potential of the electrostatic repulsion component C is 28~35 mV. The electrostatic repulsion component C provides a mild and stable electrostatic repulsion force, balances the attractive forces between particles, inhibits secondary agglomeration, and avoids conflict between strong static electricity and the binder, making it suitable for high-solids content slurries. The electrostatic repulsion component C is selected from one or more of sulfonamide-based vinyl ether homopolymers, betaine-type sulfoacrylamide copolymers, and sulfonamide-modified polyesters.

[0043] For example, the electrostatic repulsion component C is a sulfonamide-based vinyl ether homopolymer (repeating unit as shown in Formula 7), which is a linear homopolymer obtained by cationic polymerization of N-(2-ethyleneoxyethyl)-1,3-propanesulfonamide as monomer. The repeating unit has a vinyl ether as the main chain and closed-ring five-membered sulfonamide functional groups as side links. Compared with traditional sulfonate dispersants such as polystyrene sulfonic acid (PSS), the sulfonamide-based vinyl ether homopolymer of the present invention has three core advantages: a) More suitable electrostatic type: The present invention is a non-dissociative double layer with mild electrostatic repulsion and does not electrostatically adsorb with the binder, while PSS is a dissociative -SO3 - a) It easily combines with the polar groups of PVDF / CMC, leading to slurry flocculation; b) It has higher structural stability: the present invention has a five-membered heterocyclic closed-ring structure, which is resistant to hydrolysis and high shear, and the functional groups do not fall off, while PSS is an open-chain sulfonate, which easily combines with Fe on the LFP surface. 2+ / Li + The combination leads to electrostatic decay; c. Better slurry compatibility: The ether bond backbone of this invention has high compatibility with both NMP and aqueous phases, and is suitable for slurries with a high solids content of >65%, while the PSS backbone is a benzene ring with strong hydrophobicity, which is prone to self-aggregation under high solids content, resulting in increased slurry viscosity.

[0044] The electrostatic repulsion component C is a betaine-type sulfoacrylamide copolymer (repeating unit as shown in Formula 8), a random copolymer of acrylamide as the base monomer and 3-(N,N-dimethylammonium)propyl sulfonate acrylamide as the zwitterionic functional monomer, prepared by free radical solution copolymerization. The molar ratio of acrylamide to betaine-type sulfoacrylamide is m:n=2:1~4:1 (preferably 3:1), the degree of polymerization is q=m+n=20~30, and the number average molecular weight of the copolymer is 2500~3500g / mol. The core electrostatic functional group is 3-(N,N-dimethylammonium)propyl sulfonate, which is a zwitterionic functional group with intramolecular charge balance, without free ion precipitation, forming an ionic double layer that is mild and stable, with excellent compatibility with waterborne CMC / PVA adhesives, and is resistant to high shear and hydrolysis, making it suitable for the sanding / storage process of lithium battery paste.

[0045] The interface compatibility component D is a compound and / or polymer having sulfoxide and / or urea-formate groups, with a number average molecular weight of 500-5000 g / mol. The interface compatibility component D optimizes the interfacial compatibility between the strong anchoring component B, the electrostatic repulsion component C, and the solvent A, as well as the binder and the carbon layer on the LFP surface, reducing the risk of phase separation, lowering the viscosity of high-solids content slurries, and enhancing the overall stability of the dispersion system. The interface compatibility component D is selected from one or more of sulfoxide ethyl ether, sulfoxide propyl ether, and urea-formate polyether.

[0046] For example, the interfacial compatibility component D is a sulfoxide ethyl ether grafted acrylic acid-NVP copolymer (sulfoxide ethyl / propyl ether structure as shown in Formula 10), which belongs to a moderately polar nonionic interfacial compatibility polymer. The core structure is the acrylic acid-NVP random copolymer backbone, and the side chains are grafted with 30~50% sulfoxide ethyl / propyl ether (structure -CO-(CH2)) via COC covalent bonds. n-SO-CH3, n=2 / 3, representing ethyl / propyl groups respectively), with sulfoxide (-SO-) as the core interfacial compatibility site. Compared to traditional interfacial compatibility functional groups commonly used in lithium battery pastes, such as simple ether groups, ester groups, and alcohol hydroxyl groups, the core advantages of this sulfoxide-based ethyl ether graft copolymer are: a) Precise polarity matching: Simple ether / ester groups have too low polarity (ε<20), and alcohol hydroxyl groups have too high polarity (ε>80), neither of which can match the three-phase polarity gradient; sulfoxide groups have moderate polarity (ε=30~35), which is the "optimal polar bridge" at the three-phase interface of LFP paste, improving the interfacial tension reduction effect by more than 50%; b) No functional interference: Traditional ionic interfacial functional groups such as carboxyl groups and sulfonates will interfere with the strongly anchoring component B. The coordination sites and the double layer of electrostatic repulsion component C are subject to charge interaction, interfering with the dispersion effect; the sulfoxide ethyl / propyl ether is non-ionic and has no charge interference, ensuring ternary synergy; c. Dual system compatibility: simple ether groups are only suitable for oily systems, and alcohol hydroxyl groups are only suitable for aqueous systems; the sulfoxide ethyl / propyl ether of this invention can control compatibility through alkyl chains to achieve compatibility in both water and oil systems, without the need to design two interface functional groups separately; 3. Superior shear resistance: the bond energy of the COC covalent bond is much higher than that of the traditional ester bond, which is resistant to high shear and hydrolysis, and no functional groups are shed during long-term storage of the slurry, resulting in long-lasting interfacial compatibility.

[0047] The interfacial compatibility component D is polyethylene glycol monomethyl ether urea formate, preferably α-methoxy-ω-urea formate polyoxyethylene ether (as shown in Formula 11), which is a nonionic hydrogen-bonded interfacial compatibility polymer with a core structure of CH3O-(CH2CH2O). n -O-CO-N(CO-NH-R)-H (n=5~10, R is isophorone group), with a number average molecular weight of 1500~2500 g / mol. Its core interfacial active site is the urethane group (-O-CO-N(CO-NH-)-), containing two sets of NH, two sets of C=O and CO ether bonds, and multiple hydrogen bond sites. It can form a stable multiple hydrogen bond network with LFP surface, binder and solvent, significantly reducing the interfacial tension of the three phases. The low molecular weight polyether segments (n=5~10) improve the solubility and molecular chain extension of the polymer in the NMP / water dual system. It forms a ternary synergy with the anchoring function of strong anchoring component B and the electrostatic repulsion function of electrostatic repulsion component C. It is suitable for high solids oil content PVDF-NMP system and can completely eliminate slurry viscosity rebound and coating pinhole defects.

[0048]

[0049]

[0050] In this invention, the mass ratio of the strong anchoring component B, the electrostatic repulsion component C, and the interfacial compatibility component D in the compound lithium iron phosphate dispersant is 1:0.5~1.5:0.3~1, preferably 1:1.2:0.8, which can significantly reduce the viscosity of the slurry.

[0051] In this invention, the compounded lithium iron phosphate dispersant further contains solvent A, which can dissolve and disperse the strong anchoring component B, the electrostatic repulsion component C, and the interfacial compatibility component D to facilitate subsequent slurry preparation. Simultaneously, the solid content of the dispersant can be adjusted to suit different slurry systems. For example, it can be selected from one or more of N-methylpyrrolidone, deionized water, and dimethyl sulfoxide. When solvent A is included, the total solid content of the compounded lithium iron phosphate dispersant is 10-20%, facilitating precise control of the effective dispersant content in the slurry. The weight of solvent A is 3-8 times the total mass of the strong anchoring component B, the electrostatic repulsion component C, and the interfacial compatibility component D, accounting for 80-90% of the total mass of the compounded lithium iron phosphate dispersant.

[0052] This invention presents a compound lithium iron phosphate dispersant that constructs a ternary synergistic system with strong anchoring, stable electrostatics, and excellent interface. The core components complement each other and synergistically enhance each other's effects. The oxazolidinone group of the strong anchoring component B binds to the Fe atoms on the lithium iron phosphate surface via N and O atoms. 2+ A six-membered coordination ring is formed, with the hydrazide group interacting with Fe via -NHNH2. 2+ A stable chelated structure is formed, with a grafting rate of ≥90%, ensuring an adsorption strength that is more than 30% higher than that of traditional dispersants, effectively avoiding particle agglomeration caused by dispersant desorption; the electrostatic repulsion component C provides a mild and stable electrostatic repulsion force of 28~35mV, which not only inhibits secondary particle agglomeration but also does not generate electrostatic conflict with the binder, making it suitable for the preparation of high solids content slurries; the sulfoxide group of the interfacial compatibility component D is a moderately polar functional group, which is the "optimal polar bridge" at the three-phase interface of the slurry, and the urea carbamate group contains multiple hydrogen bond sites. Both can effectively reduce the interfacial tension of the slurry, optimize the interfacial compatibility between the dispersant and the solvent, binder, and carbon layer on the surface of lithium iron phosphate, and reduce the risk of phase separation.

[0053] Secondly, the present invention provides a method for preparing a compound lithium iron phosphate dispersant as described herein, the preparation method comprising: 1) Mix the strong anchoring component B, the electrostatic repulsion component C, and the interfacial compatibility component D to obtain a mixture; Optionally, 2) add solvent A to the mixture obtained in step 1), and stir at 300-600 rpm for 30-60 min at a temperature of 25-60℃ to obtain a premixed system; 3) Stir the mixture from step 1) or the premixed system from step 2) at a temperature of 40~70℃ and a speed of 300~600rpm for 60~120min, and then cool to obtain the compound lithium iron phosphate dispersant.

[0054] The preparation method of the compound lithium iron phosphate dispersant of the present invention is simple and convenient, requiring no complex chemical reactions or special equipment, and is easy to industrialize.

[0055] In this invention, in step 1), the mass ratio of the strong anchoring component B, the electrostatic repulsion component C, and the interfacial compatibility component D in the compound lithium iron phosphate dispersant is 1:0.5~1.5:0.3~1.0.

[0056] In this invention, the selection of solvent A, strong anchoring component B, electrostatic repulsion component C, and interface compatibility component D is the same as above, and will not be repeated here.

[0057] Thirdly, the present invention provides an application of the compound lithium iron phosphate dispersant as described in the present invention in the preparation of lithium iron phosphate cathode slurry.

[0058] The application of the compound lithium iron phosphate dispersant of the present invention in the preparation of lithium iron phosphate cathode slurry results in slurry with high solid content, low viscosity and good stability, which can significantly improve the quality of electrode preparation and lithium battery performance.

[0059] Fourthly, the present invention provides a lithium iron phosphate cathode slurry, wherein the lithium iron phosphate cathode slurry is composed of the following components by mass: 57-67 parts of lithium iron phosphate base material, 1-8 parts of conductive agent, 1-5 parts of binder, 0.06-2 parts of dispersant, and 30-40 parts of slurry solvent. The dispersant is a compound lithium iron phosphate dispersant as described in this invention. In this invention, the lithium iron phosphate base material is selected from one or more of lithium iron phosphate, Mg-doped lithium iron phosphate, manganese iron phosphate, and carbon-coated lithium iron phosphate.

[0060] In this invention, the conductive agent is not particularly limited and can be one or more of the conventional conductive agents in the art, such as conductive carbon black, carbon nanotubes, acetylene black, furnace black, carbon fiber VGCF, nano-graphite, graphite and conductive graphite.

[0061] In this invention, the adhesive is not particularly limited and can be a conventional adhesive in the art, such as one or more of polyvinylidene fluoride, carboxymethyl hydroxyethyl cellulose and polyvinyl alcohol.

[0062] In this invention, the solvent for the slurry is selected from one or more of N-methylpyrrolidone, deionized water, and dimethyl sulfoxide. The amount of solvent used is sufficient to give the paste viscosity and fluidity, and to ensure that the lithium iron phosphate base, conductive agent, binder, and dispersant are mixed evenly.

[0063] In this invention, the solid content of the lithium iron phosphate cathode slurry is ≥60%, and the viscosity is ≤10000 mPa·s.

[0064] Since the improvement of this invention lies only in the compounded lithium iron phosphate dispersant, the improved preparation method of the lithium iron phosphate cathode slurry is conventional in the art. For example, the binder is first dissolved in a solvent, and the compounded dispersant is added and stirred for 30-40 minutes to ensure uniform dispersion of the dispersant. Then, the conductive agent and LFP material are added in sequence, and the mixture is initially mixed by stirring at a low speed of 300-500 rpm for 40-60 minutes. The initial agglomeration is broken by high-speed shearing at 1500-2500 rpm for 80-120 minutes to obtain a uniform and stable LFP cathode slurry, which is suitable for existing industrial production processes.

[0065] 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.

[0066] Preparation Example 1: Synthesis of oxazolidinone acrylate homopolymer: 2-(2-oxo-1,3-oxazolidine-3-yl)ethyl acrylate was washed three times with 5% sodium hydroxide aqueous solution to remove polymerization inhibitors, washed with deionized water until neutral, dried over anhydrous sodium sulfate, and purified by vacuum distillation; N-methylpyrrolidone (NMP) was dried over molecular sieves until the moisture content was ≤0.05%; 240g of NMP and 80g of purified monomer were added to a 500mL four-necked flask, stirred to dissolve, and then 0.96g of azobisisobutyronitrile (AIBN) initiator and 1 0.2g of dodecanethiol chain transfer agent was used, and the reaction was carried out under nitrogen bubbling for 35 minutes to maintain a slight positive pressure. The temperature was raised to 70℃, and the reaction was stirred for 8 hours at 350 rpm under nitrogen protection throughout the process. No gelation or side reactions occurred. After the reaction solution was cooled, it was precipitated with anhydrous ethanol, filtered, washed three times with anhydrous ethanol, and dried under vacuum at 55℃ for 10 hours to obtain a white powdery homopolymer, namely oxazolidinone acrylate homopolymer, denoted as B1. The finished product weighed 76g, with a yield of 95%.

[0067] Gel permeation chromatography (GPC) was used with N,N-dimethylformamide (DMF) as the reagent and narrow-distribution polymethyl methacrylate (PMMA) as the standard (matching the structure of the polymer to be tested). 15 mg of the dried polymer was weighed and placed in a 10 mL volumetric flask. The GPC mobile phase was added and the solution was brought to the mark. The solution was sonicated for 10 min until completely dissolved, and then filtered through a 0.22 μm organic phase filter membrane to obtain the test sample solution. The column temperature was 40 °C, the mobile phase flow rate was 1.0 mL / min, the injection volume was 20 μL, and the test time was 20 min. The number-average molecular weight of polymer B1 was calculated to be 3800 g / mol using the calibration curve. The degree of polymerization, q = 22, was calculated by subtracting the mass of the end-group residues from the number-average molecular weight and dividing by the molar mass of the repeating unit.

[0068] Preparation Example 2: Synthesis of hydrazide methacrylate-styrene copolymer: Ethyl methacrylhydrazide (terminal group -NHNH2, non-acetylated structure) and styrene were purified by vacuum distillation to remove polymerization inhibitors. NMP was dried to ≤0.05% moisture content using molecular sieves. 225g of NMP was added to a 500mL four-necked flask, and nitrogen was bubbled throughout the process. Then, 1 / 3 of the total amount of ethyl methacrylhydrazide and styrene mixed monomers (total feed: 72.5g ethyl methacrylhydrazide, 10.4g styrene, molar ratio 4:1) was added. After stirring to dissolve, 1.02g of AIBN initiator and 0.51g of n-dodecyl mercaptan chain transfer polymer were added. The mixture was purged with nitrogen for 35 minutes to maintain a slight positive pressure. The temperature was raised to 70°C, and the remaining 2 / 3 of the mixed monomers were added dropwise over a period of 4 hours while maintaining the temperature and stirring. After the addition was complete, the reaction was continued at the temperature for another 6 hours, for a total reaction time of 10 hours. The reaction was carried out at a speed of 380 rpm under nitrogen protection throughout the process. No gelation or side reactions occurred, and a random copolymer structure was formed. After the reaction solution was cooled, it was precipitated with anhydrous ethanol, filtered, washed three times with anhydrous ethanol, and dried under vacuum at 55°C for 10 hours to obtain a white powdered copolymer, namely hydrazide methacrylate-styrene copolymer, denoted as B2, with a finished product weight of 78g.

[0069] Using the method of Preparation Example 1, the number-average molecular weight of B2 was determined to be 4500 g / mol.

[0070] The proton nuclear magnetic resonance (NMR) method was used, with deuterated chloroform as the reagent, purity ≥99.8%. 15 mg of dried polymer B2 was weighed and placed in a 5 mm NMR tube, along with 0.5 mL of the deuterated reagent. The mixture was sonicated for 10 min until completely dissolved, yielding a clear and transparent test solution. The test parameters were: temperature 25℃, pulse width 45°, relaxation time 1 s, and 16 scans. The molar ratio of the two monomers was calculated to be 4:1 based on the integrated area ratio of the characteristic hydrogens of the benzene ring to the characteristic hydrogens of the ortho-methylene group of the hydrazide. The grafting rate of the hydrazide group was calculated to be ≥92% based on the integrated percentage of the characteristic hydrogens of the -NH2 terminal group (δ=4.2 ppm).

[0071] The grafting rate mentioned above is the molar grafting rate, defined as the number of moles of characteristic functional groups grafted / the total number of moles of repeating units in the polymer matrix × 100%.

[0072] Preparation Example 3: Synthesis of Oxazolidinone-Modified Polyethers: Polyethylene glycol monomethyl ether (mPEG, number average molecular weight 3300 g / mol) was purified by vacuum distillation to remove water. Dichloromethane was dried to ≤0.02% moisture content using molecular sieves. Sodium hydroxide and epichlorohydrin were of analytical grade. 100 g of purified mPEG and 400 g of dried dichloromethane were added to a 1000 mL four-necked flask. After stirring and dissolving, 12 g of powdered sodium hydroxide was added. The system was purged with nitrogen for 25 min, maintaining a slight positive pressure. 15 g of epichlorohydrin was slowly added dropwise at room temperature. The reaction time was 2 hours, and the rotation speed was 350 rpm throughout. After the addition was complete, the reaction was kept at room temperature and stirred for 12 hours under nitrogen protection throughout. After the reaction was completed, the sodium chloride byproduct was removed by filtration. The filtrate was washed three times with deionized water until neutral. The organic phase was dried with anhydrous sodium sulfate, and dichloromethane was removed by vacuum distillation. 800 mL of anhydrous diethyl ether was added to precipitate the product. The product was filtered and dried under vacuum at 35°C for 8 hours to obtain a white waxy solid, namely epoxy-terminated polyethylene glycol monomethyl ether (mPEG-EO). The product weight was 94 g, and the yield was 94%.

[0073] The mPEG-EO and 2-isocyanate-ethyl methacrylate (IEM) prepared above were purified by vacuum distillation. N-methylpyrrolidone (NMP) was dried to ≤0.05% moisture content using molecular sieves. The polymerization inhibitor hydroquinone monomethyl ether (MEHQ) and the cycloaddition catalyst lithium bromide (LiBr) were both analytical grade. 100g of mPEG-EO was added to a 500mL four-necked flask, 314g of NMP was added and stirred to dissolve, 0.05g of MEHQ polymerization inhibitor was added, and the system was purged with nitrogen for 35min, maintaining a slight positive pressure. Add 0.32g of lithium bromide catalyst, heat to 140℃, and slowly add 4.8g of IEM dropwise over 1.5h at a constant speed of 350rpm. After the addition is complete, maintain the temperature at 140℃ and stir for 10h under nitrogen protection throughout the process. No gelation or side reactions occurred. After the reaction solution is cooled to room temperature, add 800mL of anhydrous ethanol to precipitate the product. Filter the product, wash three times with anhydrous ethanol, and dry under vacuum at 60℃ for 12h to obtain a white waxy solid product, namely oxazolidinone-modified polyether, denoted as B3. The product weight is 98g, and the yield is 93.5%.

[0074] Using the method of Preparation Example 1, the number-average molecular weight of B3 was determined to be 4200 g / mol; The 1H NMR spectroscopy method was used with deuterated chloroform as a reagent. The grafting rate of the oxazolidinone group was calculated to be 92% by the integral area ratio of the characteristic hydrogens of the oxazolidinone ring to the characteristic hydrogens of the mPEG backbone.

[0075] Preparation Example 4: Synthesis of sulfonamide vinyl ether homopolymers: N-(2-Ethyloxyethyl)-1,3-propanesulfonamide (containing a cationically polymerizable vinyl ether group and a closed-ring sulfonamide group) was purified twice by recrystallization with anhydrous diethyl ether, and the solvent was removed by vacuum drying. Dichloromethane was dried to a moisture content of ≤0.02% using molecular sieves. A 500mL four-necked flask was used as the reaction vessel, and the entire process was carried out under nitrogen protection in an anhydrous and oxygen-free environment. 288g of dried dichloromethane and 96g of purified monomer were added to the flask, stirred to dissolve, and then cooled to 0℃. The mixture was then slowly added dropwise. 1.2 g of boron trifluoride diethyl ether complex cationic initiator was added dropwise over 30 min at a stirring speed of 380 rpm. After the addition was complete, the mixture was kept at 0 °C and stirred for 4 h. The reaction was terminated by adding 5 mL of methanol. The reaction solution was concentrated by rotary evaporation, and 750 mL of anhydrous diethyl ether was added to precipitate the product. After filtration, the product was washed three times with anhydrous diethyl ether and dried under vacuum at 55 °C for 10 h to obtain a white powdery homopolymer, namely sulfonamide vinyl ether homopolymer, denoted as C1. The weight of the finished product was 85 g, and the yield was 92%.

[0076] Using the method of Preparation Example 1, the number-average molecular weight of C1 was determined to be 2800 g / mol.

[0077] The degree of polymerization q=14 was calculated by using nuclear magnetic resonance hydrogen spectroscopy with deuterated dimethyl sulfoxide as a reagent, based on the integrated area of ​​the characteristic hydrogen of the vinyl ether main chain and the characteristic hydrogen of the ortho-methylene group of the sulfonamide ring.

[0078] Preparation Example 5: Synthesis of betaine-type sulfoacrylamide copolymer: N,N-Dimethylacrylamide (DMAA) and 3-[(2-acrylamido)propyl]dimethylammonium propanesulfonate (SBAA) were purified by vacuum distillation / recrystallization, respectively. Anhydrous ethanol was dried to ≤0.05% moisture content using molecular sieves. 266g of anhydrous ethanol was added to a 500mL four-necked flask, and nitrogen was bubbled throughout the process. One-third of the total amount of the DMAA and SBAA mixture (total feed: 45.7g DMAA, 43.1g SBAA, molar ratio 3:1) was added first, and after stirring to dissolve, 1.07g AIBN initiator and 0.53g n-dodecyl mercaptan chain were added. The transfer agent was used, and the system was purged with nitrogen for 35 minutes to maintain a slight positive pressure. The temperature was raised to 70°C, and the remaining 2 / 3 of the mixed monomers were added dropwise at a uniform rate over 4 hours while maintaining the temperature and stirring. After the addition was completed, the reaction was continued at the temperature for another 6 hours, for a total reaction time of 10 hours. The reaction was carried out at a speed of 380 rpm under nitrogen protection throughout the process. No gelation or side reactions occurred, and an amphoteric random copolymer structure was formed. After the reaction solution was cooled, it was precipitated with anhydrous diethyl ether, filtered, washed three times with anhydrous ethanol, and dried under vacuum at 55°C for 10 hours to obtain a white powdery copolymer, namely betaine-type sulfoacrylamide copolymer, denoted as C2. The product weight was 80 g, and the yield was 90%.

[0079] Using the method of Preparation Example 1, the number-average molecular weight of C2 was determined to be 3200 g / mol.

[0080] Using the 1H NMR spectroscopy method of Preparation Example 2, with deuterated methanol as the reagent, the molar ratio of the two monomers was calculated to be 3:1 and the overall degree of polymerization q=26 by the integral area ratio of the characteristic hydrogen of dimethyl DMAA (δ≈2.9ppm) to the characteristic hydrogen of ortho-methylene sulfonate of SBAA (δ≈2.8ppm).

[0081] Preparation Example 6: Synthesis of sulfoxide ethyl ether: Step 1: Purify 2-methylthioethanol by vacuum distillation, remove oxygen by bubbling with deionized water and nitrogen, and adjust the pH of the system to 8-9; add 200g deionized water, 50g 2-methylthioethanol, 2.5g sodium tungstate catalyst, and 1.5g sodium bicarbonate pH adjuster to a 500mL four-necked flask, purge with nitrogen for 25min, and maintain a slight positive pressure in the system; control the temperature at 0-5℃, and very slowly add 45g of 30% hydrogen peroxide solution (thioether to hydrogen peroxide molar ratio 1:1.05), adding dropwise... After 3 hours of dropwise addition, the temperature was raised to 10°C and maintained for 4 hours, with a stirring speed of 300 rpm throughout the process to strictly prevent excessive oxidation to sulfone. The residual oxidant was reacted off with 20 mL of saturated sodium sulfite, the product was extracted with 150 mL of dichloromethane, dried with 10 g of anhydrous sodium sulfate, and purified by vacuum distillation to obtain a colorless and transparent liquid 2-hydroxyethylmethyl sulfoxide (sulfoxide ethyl alcohol). The product weighed 45 g, with a yield of 90%. Gas chromatography analysis showed that the sulfoxide purity was ≥98% and there were no sulfone byproducts.

[0082] Step 2: Synthesis of sulfoxide-based graft copolymer: Acrylic acid and N-vinylpyrrolidone (NVP) were purified by vacuum distillation, and 1,4-dioxane was dried to ≤0.05% moisture content using molecular sieves. 300g of 1,4-dioxane, 36g of acrylic acid, and 24g of NVP were added to a 500mL four-necked flask. After stirring and dissolving, 0.72g of AIBN initiator was added. Nitrogen gas was purged for 35min, the temperature was raised to 70℃, and the reaction was maintained at this temperature with stirring for 6h to obtain the acrylic acid-NVP random copolymer prepolymer. Add 30g of the 2-hydroxyethyl methyl sulfoxide and 0.3g of p-toluenesulfonic acid catalyst prepared above to the prepolymer solution, heat to 90℃, and maintain the esterification reaction for 8h under nitrogen protection throughout. Separate the generated water using a water separator. After cooling the reaction solution, precipitate with n-hexane, filter, wash three times with anhydrous ethanol, and vacuum dry at 50℃ for 12h to obtain a white powder polymer. The finished white powder polymer product, namely sulfoxide ethyl ether grafted acrylic acid-NVP copolymer, is denoted as D1, with a product weight of 82g and a yield of 91%.

[0083] Using the method of Preparation Example 1, the number-average molecular weight of D1 was determined to be 1200 g / mol.

[0084] Preparation Example 7: Synthesis of Urea Carbamate Polyether: Polyethylene glycol monomethyl ether (mPEG, number average molecular weight 1000 g / mol) was purified by vacuum distillation at 120 °C for 3 h until the water content was ≤0.02%. Isophorone diisocyanate (IPDI) was purified by vacuum distillation, and NMP was dried with molecular sieves until the water content was ≤0.05%. 324 g of NMP and 100 g of purified mPEG were added to a 500 mL four-necked flask, stirred and dissolved, and then 0.222 g of dibutyltin dilaurate (DBTDL) catalyst was added. The system was purged with nitrogen for 35 min, maintaining a slight positive pressure. The temperature was raised to 50 °C, and 22.2 g of IPDI was slowly added dropwise over 1 h. After the addition was completed, the system was kept at 50 °C. After reacting for 3 hours, a prepolymer of urethane-terminated polyether (a semi-addition product with no free -NCO residue) was obtained. 0.1 g of DBTDL catalyst was added to the prepolymer, and the temperature was raised to 90°C. The mixture was stirred and kept at this temperature for 6 hours to allow the urethane-terminated groups to undergo an addition reaction with the remaining -NCO of IPDI, generating a urethane-formaldehyde structure. The entire process was carried out under nitrogen protection, with no gelation or side reactions. After cooling the reaction solution to room temperature, it was precipitated with anhydrous ethanol, filtered, washed three times with anhydrous ethanol, and dried under vacuum at 55°C for 10 hours to obtain a white, waxy polyether product, namely, a urethane-terminated polyethylene glycol monomethyl ether, denoted as D2. The product weight was 100 g, with a yield of 93%.

[0085] Using the method of Preparation Example 1, the number-average molecular weight of D2 was determined to be 1600 g / mol.

[0086] Example 1: The compound lithium iron phosphate dispersant in this example is a 4-component system, which is suitable for conventional LFP.

[0087] 1. Dispersant Preparation Weigh precisely according to the mass ratio B1:C1:D1=1:1:0.5 and add to a sealed container: B1: 10 parts of oxazolidinone acrylate homopolymer (number average molecular weight 3800 g / mol); C1: 10 parts of sulfonamide vinyl ether homopolymer (number average molecular weight 2800 g / mol); D1: 5 parts of sulfoxide ethyl ether (number average molecular weight 1200 g / mol); Add 125 parts of solvent A (NMP) (5 times the total mass of B1+C1+D1), stir at 40℃ for 40 min at 500 rpm to ensure initial uniform mixing; heat to 60℃, keep warm and stir for 90 min, cool to room temperature, and filter through a 1 μm filter membrane to obtain a compound lithium iron phosphate dispersant with a solid content of 16.7%, denoted as F1.

[0088] Structural characterization: by Figure 1As can be seen from the infrared spectrum, the characteristic peaks of the compound lithium iron phosphate dispersant F1 in this embodiment are assigned to ~3400 cm⁻¹. -1 (-NH- stretching vibration), ~1700 cm -1 (Oxazolidinone C=O stretching vibration), ~1300 cm -1 (Sulfolactam-SO2- stretching vibration), ~1100 cm -1 (sulfoxide-SO- stretching vibration), it can be seen that the key functional groups of the compound lithium iron phosphate dispersant F1 in this embodiment are all present.

[0089] 2. Preparation of Lithium Iron Phosphate Cathode Slurry Weigh the following by weight: LFP material (64 parts, particle size 1.0 μm, carbon content 2%), conductive carbon black-carbon nanotube composite conductive agent (2 parts, mass ratio 1:1), PVDF binder (2 parts), composite lithium iron phosphate dispersant F1 (2 parts), NMP (30 parts).

[0090] PVDF was dissolved in NMP and stirred for 30 min until completely dissolved; conductive agent and compound lithium iron phosphate dispersant F1 were added and stirred at low speed for 40 min; LFP material was added and stirred at low speed for 50 min and then sheared at high speed for 100 min to obtain lithium iron phosphate cathode slurry with a solid content of 68.3% and an addition amount of compound lithium iron phosphate dispersant F1 of 0.49%.

[0091] Example 2: The compound lithium iron phosphate dispersant in this example is a 3-component system, which is suitable for Mg-doped LFP.

[0092] 1. Dispersant Preparation Weigh precisely the ingredients according to the mass ratio B2:C2:D2 = 1:0.8:0.7 and add them to a sealed container. B2: 10 parts of hydrazide methacrylate-styrene copolymer (number average molecular weight 4500 g / mol, m:n=4:1); C2: 8 parts of betaine-type sulfoacrylamide copolymer (number average molecular weight 3200 g / mol, m:n=3:1); D2: 7 parts of urea-formaldehyde polyether (number average molecular weight 1600 g / mol); Stir at 30℃ for 50 min at 400 rpm to ensure uniform mixing of components; heat to 50℃, keep warm and stir for 100 min, cool to room temperature to obtain solid powdered compound lithium iron phosphate dispersant, denoted as F2; Structural characterization: by Figure 2 As can be seen from the infrared spectrum, the characteristic peaks of the compound lithium iron phosphate dispersant F2 in this embodiment are assigned to ~3100 cm⁻¹. -1(hydrazide-NHNH2 stretching vibration), ~1660 cm -1 (Amide group C=O stretching vibration), ~1500 cm -1 (Betaine type - N) + (CH3)2 bending vibration), ~1300 cm -1 (Urea carbamate group -CONH- stretching vibration), it can be seen that the key functional groups of the compound lithium iron phosphate dispersant F2 in this embodiment are present.

[0093] 2. Preparation of Lithium Iron Phosphate Cathode Slurry Weigh the following by weight: Mg-doped LFP material (57.94 parts, particle size 0.8 μm, carbon content 3%), conductive carbon black (1 part), CMC binder (1 part), compound lithium iron phosphate dispersant F2 (0.06 parts), and deionized water (40 parts).

[0094] CMC was dissolved in deionized water, and compound lithium iron phosphate dispersant F2 was added and stirred for 40 min until completely dispersed. A conductive agent was added and stirred at low speed for 50 min. LFP material was added and stirred at low speed for 60 min and then sheared at high speed for 110 min to obtain lithium iron phosphate cathode slurry with a solid content of 60% and an addition amount of compound lithium iron phosphate dispersant F2 of 0.1%.

[0095] Example 3: The compound lithium iron phosphate dispersant in this example is a 4-component system. 1. Dispersant Preparation Weigh out the appropriate amount of B3:C2:D2 by mass ratio of 1:1.2:0.8 and add it to a sealed container. B3: 10 parts of oxazolidinone-modified polyether (number average molecular weight 4200 g / mol, oxazolidinone grafting rate 90%). C2: 12 parts of betaine-type sulfoacrylamide copolymer (number average molecular weight 3200 g / mol, m:n=3:1); D2: 8 parts of urea-formaldehyde polyether (number average molecular weight 1600 g / mol); Add 150 parts of solvent A (deionized water) (5 times the total mass of B3+C2+D2), stir at 50℃ for 50 min at 600 rpm; heat to 65℃, keep warm and stir for 110 min, cool to room temperature, and filter through a 1 μm filter membrane to obtain a compound lithium iron phosphate dispersant with a solid content of 16.7%, denoted as F3.

[0096] Structural characterization: by Figure 3 As can be seen from the infrared spectrum, the characteristic peaks of the compound lithium iron phosphate dispersant F3 in this embodiment are assigned to ~3400 cm⁻¹. -1 (hydrazide-NHNH2 stretching vibration), ~1660 cm-1 (Amide group C=O stretching vibration), ~1500 cm -1 (Betaine type - N) + (CH3)2 bending vibration), ~1300 cm -1 (Urea carbamate group -CONH- stretching vibration), it can be seen that the key functional groups of the compound lithium iron phosphate dispersant F3 in this embodiment are present.

[0097] 2. Preparation of Lithium Iron Phosphate Cathode Slurry Weigh the following by weight: LFP material (61.1 parts, particle size 0.6μm, carbon content 2.5%), carbon nanotube conductive agent (1 part), PVA binder (1 part), compound lithium iron phosphate dispersant F3 (1.9 parts), and deionized water (35 parts).

[0098] PVA was dissolved in deionized water, and compound lithium iron phosphate dispersant F3 was added and stirred for 35 min; carbon nanotubes were added and stirred at low speed for 45 min; LFP material was added and stirred at low speed for 55 min and then sheared at high speed for 120 min to obtain lithium iron phosphate cathode slurry with a solid content of 63% and an addition amount of compound lithium iron phosphate dispersant F3 of 0.5%.

[0099] Example 4: The compound lithium iron phosphate dispersant in this example is a 4-component system, which is suitable for the LMFP dual system.

[0100] 1. Dispersant preparation (Mn for LMFP) 2+ / Fe 2+ Bimetallic coordination design) Weigh precisely the ingredients according to the mass ratio B2:C2:D1=1:1.2:0.9 and add them to a sealed container. B2: 10 parts of hydrazide methacrylate-styrene copolymer (number average molecular weight 4500 g / mol, m:n=4:1); C2: 12 parts of betaine-type sulfoacrylamide copolymer (number average molecular weight 3200 g / mol, m:n=3:1); D1: 9 parts of sulfoxide ethyl ether (number average molecular weight 1200 g / mol); Add 155 parts of solvent A (NMP) (5 times the total mass of B2+C2+D1) and stir at 35℃ for 50 min at 550 rpm; heat to 65℃ and stir for 110 min; cool to room temperature and filter through a 1 μm filter membrane to obtain a compound lithium iron phosphate dispersant with a solid content of 16.7%, denoted as F4.

[0101] Structural characterization: by Figure 4 The infrared spectrum shows that the characteristic peaks of the compound lithium iron phosphate dispersant F4 in this embodiment are assigned to ~3400 cm⁻¹.-1 (hydrazide-NHNH2 stretching vibration), ~1650 cm -1 (Amide group C=O stretching vibration), ~1300 cm -1 (Betaine type - N) + (CH3)2 bending vibration), ~1100 cm -1 (sulfoxide-SO- stretching vibration), it can be seen that the key functional groups of the compound lithium iron phosphate dispersant F4 in this embodiment are present.

[0102] 2. Preparation of Lithium Iron Phosphate Cathode Slurry Weigh the following by weight: LMFP material (59.1 parts, particle size 0.9μm, Mn doping 15%, carbon content 2.5%), carbon nanotube-conductive carbon black composite conductive agent (2 parts, mass ratio 1:2), PVDF binder (2 parts), composite lithium iron phosphate dispersant F4 (1.9 parts), and NMP (35 parts).

[0103] PVDF was dissolved in NMP and stirred for 35 min; a conductive agent and compound lithium iron phosphate dispersant F4 were added and stirred at low speed for 45 min; LMFP was added and stirred at low speed for 55 min and then sheared at high speed for 100 min to obtain lithium iron phosphate cathode slurry with a solid content of 65% and an addition amount of compound lithium iron phosphate dispersant F4 of 0.5%.

[0104] Example 5: The compound lithium iron phosphate dispersant in this example is a 3-component system, suitable for low carbon content LFP.

[0105] 1. Dispersant Preparation Weigh precisely the ingredients according to the mass ratio B3:C1:D1=1:1.2:0.9 and add them to a sealed container. B3: 10 parts of oxazolidinone-modified polyether (number average molecular weight 4200 g / mol, oxazolidinone grafting rate 90%). C1: 12 parts of sulfonamide vinyl ether homopolymer (number average molecular weight 2800 g / mol, degree of polymerization q=14); D1: 9 parts of sulfoxide propyl ether (number average molecular weight 1400 g / mol); Control the temperature at 35℃, start stirring at 450 rpm, and mix for 60 minutes to ensure that the powder is free of lumps and is mixed evenly; raise the temperature to 55℃, keep stirring for 110 minutes to allow hydrogen bonds and van der Waals forces to form between the molecules of each component; cool naturally to room temperature to obtain a white, free-flowing powdered compound lithium iron phosphate dispersant, denoted as F5.

[0106] Structural characterization: by Figure 5As can be seen from the infrared spectrum, the characteristic peaks of the compound lithium iron phosphate dispersant F5 in this embodiment are assigned to ~1700 cm⁻¹. -1 (Oxazolidinone C=O stretching vibration), ~1320 cm -1 (Sulfolactam-SO2- stretching vibration), ~1100 cm -1 (sulfoxide-SO- stretching vibration), it can be seen that the key functional groups of the compound lithium iron phosphate dispersant F5 in this embodiment are present.

[0107] 2. Preparation of Lithium Iron Phosphate Cathode Slurry Weigh the following by weight: LFP material (60.8 parts, particle size 0.9 μm, carbon content 1.3%), carbon nanotubes (2 parts), PVA binder (2 parts), compound lithium iron phosphate dispersant F5 (0.2 parts), and NMP (35 parts).

[0108] PVA binder was added to deionized water and stirred at 50°C for 40 minutes until completely dissolved, forming a transparent binder solution. Compound lithium iron phosphate dispersant F5 was added, and the temperature was maintained at 35°C while stirring for 35 minutes to ensure uniform dispersion of F5 in the binder system. Carbon nanotubes were added and stirred at low speed (400 rpm) for 50 minutes to achieve initial dispersion of the conductive agent. LFP material was added in batches, stirred at low speed (500 rpm) for 60 minutes, and then sheared at high speed (2000 rpm) for 90 minutes to obtain a uniform and stable LFP cathode slurry with a solid content of 65% and an addition amount of 0.31% of the compound lithium iron phosphate dispersant F5.

[0109] Example 6: The compound lithium iron phosphate dispersant in this example is a 4-component system, suitable for high carbon content LFP. 1. Dispersant Preparation Weigh out the following ingredients precisely and add them to a sealed container according to a mass ratio of B1:C1:D2=1:1:1: B1: 10 parts of oxazolidinone acrylate homopolymer (number average molecular weight 3800 g / mol); C1: 10 parts of sulfonamide vinyl ether homopolymer (number average molecular weight 2800 g / mol); D2: 10 parts of urea-formaldehyde polyether (number average molecular weight 1600 g / mol); Solvent A (DMSO) 150 parts (5 times the total mass of B1+C1+D2; DMSO has better wettability on carbon layers than NMP).

[0110] After stirring B1, C1, and D2 at 40℃ for 45 minutes (600 rpm), solvent A was added and mixed. The mixture was then heated to 70℃ and stirred for 120 minutes. After cooling, it was filtered to obtain a compound lithium iron phosphate dispersant with a solid content of 17.1%, denoted as F6.

[0111] Structural characterization: by Figure 6 As can be seen from the infrared spectrum, the characteristic peaks of the compound lithium iron phosphate dispersant F6 in this embodiment are assigned to ~1700 cm⁻¹. -1 (Oxazolidinone C=O stretching vibration), ~1320 cm -1 (Sulfolactam-SO2- stretching vibration), ~1100 cm -1 (sulfoxide-SO- stretching vibration), it can be seen that the key functional groups of the compound lithium iron phosphate dispersant F6 in this embodiment are present and there is no interference from impurity peaks.

[0112] 2. Preparation of Lithium Iron Phosphate Cathode Slurry Weigh the following by weight: high carbon LFP (54 parts, particle size 1.2 μm, carbon content 5%), conductive carbon black (6 parts), CMC binder (3.5 parts), compound lithium iron phosphate dispersant F6 (1.5 parts), and solvent DMSO (35 parts).

[0113] CMC was dissolved in DMSO, and compound lithium iron phosphate dispersant F6 was added and stirred for 40 min until completely dispersed. Conductive agent was added and stirred at low speed for 50 min. LFP material was added and stirred at low speed for 60 min and then sheared at high speed for 110 min to obtain lithium iron phosphate cathode slurry with a solid content of 63.8% and a dispersant addition of 0.39%.

[0114] Comparative Example 1: The method of Example 1 was carried out, except that B1, C1, and D1 were replaced with B', C', and D', respectively, while other steps and conditions remained unchanged, to obtain a compound lithium iron phosphate dispersant and a lithium iron phosphate cathode slurry. B': 10 parts of carboxyacrylate homopolymer (number average molecular weight 3000 g / mol); C': 10 parts of sodium polystyrene sulfonate (number average molecular weight 2500 g / mol); D': 5 parts of polyethylene glycol monomethyl ether (number average molecular weight 1200 g / mol).

[0115] Comparative Example 2: The method of Example 2 was carried out, except that "acylhydrazide methacrylate-styrene copolymer (number average molecular weight 4500 g / mol, m:n=4:1)" was replaced with "amino methacrylate-styrene copolymer (number average molecular weight 4500 g / mol)", while other steps and conditions remained unchanged, to obtain a compound lithium iron phosphate dispersant and lithium iron phosphate cathode slurry.

[0116] Comparative Example 3: The method of Example 3 was carried out, except that the mass ratio of B3:C2:D2=1:1.2:0.8 was replaced with the mass ratio of B3:C2:D2=1:0.3:0.2, while other steps and conditions remained unchanged, and a compound lithium iron phosphate dispersant and lithium iron phosphate cathode slurry were obtained.

[0117] Comparative Example 4: The method of Example 4 was carried out, except that “C2 betaine-type sulfoacrylamide copolymer (number average molecular weight 3200 g / mol, m:n=3:1)” was replaced with “C' sodium polystyrene sulfonate (number average molecular weight 4000 g / mol, m:n=1:1)”, and other steps and conditions were not changed, to obtain compound lithium iron phosphate dispersant and lithium iron phosphate cathode slurry.

[0118] Comparative Example 5:1, Dispersant Preparation Weigh precisely according to the mass ratio B'':C1:D1=1:1.1:0.6 and add to a sealed container: B'': 10 parts of oxazolidinone-modified polyether (grafting rate 80%, number average molecular weight 4000 g / mol); C1: 11 parts of sulfonamide vinyl ether homopolymer (same as Example 5); D1: 6 parts of sulfoxide propyl ether (same as in Example 5); Control the temperature at 35℃, start stirring at 450 rpm, and mix for 60 minutes to ensure that the powder is free of lumps and is mixed evenly; raise the temperature to 55℃, keep stirring for 110 minutes to allow hydrogen bonds and van der Waals forces to form between the molecules of each component; allow to cool naturally to room temperature to obtain a white, free-flowing powdered compound lithium iron phosphate dispersant.

[0119] 2. Preparation of Lithium Iron Phosphate Cathode Slurry The method of Example 5 was implemented, except that the dispersant was replaced and all other steps and conditions remained unchanged, to obtain lithium iron phosphate cathode slurry.

[0120] Comparative Example 6:1, Dispersant Preparation Weigh precisely according to the mass ratio B1:C1:D''=1:1:1: B1: 11 parts of oxazolidinone acrylate homopolymer (same as Example 6); C1: 11 parts of sulfonamide vinyl ether homopolymer (same as Example 6); D'': 11 parts of polyethylene glycol (number average molecular weight 2500 g / mol); Add 165 parts of solvent A (NMP).

[0121] After stirring B1, C1, and D'' at 40℃ for 45 min (600 rpm), solvent A was added and mixed. The mixture was then heated to 70℃ and stirred for 120 min. After cooling, it was filtered to obtain a compound lithium iron phosphate dispersant with a solid content of 18%.

[0122] 2. Preparation of Lithium Iron Phosphate Cathode Slurry The method of Example 6 was implemented, except that the dispersant was replaced and all other steps and conditions remained unchanged, to obtain lithium iron phosphate cathode slurry.

[0123] Comparative Example 7: The preparation steps of lithium iron phosphate cathode slurry in Example 1 were carried out, except that “compound lithium iron phosphate dispersant F1” was replaced with “common dispersant BYK25432”, and the other steps remained unchanged, and lithium iron phosphate cathode slurry was obtained.

[0124] Comparative Example 8: The preparation steps of lithium iron phosphate cathode slurry in Example 1 were carried out, except that “compound lithium iron phosphate dispersant F1” was replaced with “polyethylene glycol (PEG)”, and the other steps remained unchanged, and lithium iron phosphate cathode slurry was obtained.

[0125] Comparative Example 9: The preparation steps of lithium iron phosphate cathode slurry in Example 1 were carried out, except that “compound lithium iron phosphate dispersant F1” was replaced with “polyvinylpyrrolidone (PVP)”, and the other steps remained unchanged, and lithium iron phosphate cathode slurry was obtained.

[0126] Test Example 1: The performance of the lithium iron phosphate cathode slurries prepared in Examples 1-6 and Comparative Examples 1-9 was tested. The specific methods are as follows: Take 500 mL of lithium iron phosphate cathode slurry in a 1 L beaker and place it on the sample stage of the rheometer. Lower the rotor until it is in complete contact with the slurry, avoiding air entrainment. Start the instrument for pre-shearing at a shearing speed of 10 s. -1 The shearing time is 30s to eliminate the thixotropic effect of the slurry; after the pre-shearing, the parameters are kept stable for 60s, and the data is recorded every 10s. The average of the last 3 stable readings is taken as the initial viscosity. After the measurement is completed, the slurry is sealed and stored, and left to stand at 25°C for 24 hours. The viscosity is then measured using the same method and recorded as the 24-hour viscosity. (24h viscosity - initial viscosity) / initial viscosity × 100%, denoted as viscosity rebound rate.

[0127] The specific results are shown in Table 1.

[0128] Table 1

[0129] From the data in the table and the above content, we can see that Compared to the dispersant prepared in Example 1, the dispersant prepared in Comparative Example 1, by replacing the core functional groups of the strong anchoring component B, electrostatic repulsion component C, and interface compatibility component D in the technical solution of this invention, directly disrupts the ternary synergistic system of "strong anchoring-stable electrostatics-superior interface." Traditional carboxyl groups cannot form stable coordination rings, causing the anchoring link to fail; the conflict between the dissociated sulfonate and the binder causes an imbalance in the electrostatic link; and the low polarity of polyethylene glycol monomethyl ether cannot match the three-phase polarity gradient, causing the interface link to break down. The three components lack synergistic effect, leading to a surge in slurry viscosity and a sharp increase in rebound rate. In contrast, this invention achieves ternary functional complementarity through the precise adaptation of oxazolidinone, sulfonamide, and sulfoxide groups, providing the core guarantee for low viscosity and high stability.

[0130] The dispersant prepared in Comparative Example 2, compared to the dispersant prepared in Example 2, lacks bimetallic chelating function because it uses an amino group to replace the hydrazide group of the strongly anchoring component B of this invention. This causes the collapse of the ternary synergistic "anchoring basis," and the amino group can only weakly bind Fe. 2+ Unable to stabilize Mg 2+ The dispersant is prone to desorption, which prevents the mild electrostatics of the electrostatic repulsion component C from forming a uniform electric double layer. This causes the hydrogen bond network of the interfacial compatibility component D to lose support, resulting in interfacial compatibility failure. However, the bimetallic chelating effect of the hydrazide group in this invention provides a strong anchoring support for the ternary synergy, ensuring the effective functioning of both electrostatic repulsion and interfacial compatibility, thus meeting the specific requirements of Mg-doped LFP.

[0131] Compared to the dispersant prepared in Example 3, the dispersant prepared in Comparative Example 3 exhibits a "functional imbalance" in the ternary synergistic effect because the amount of electrostatic repulsion component C / interfacial compatibility component D is much lower than the optimized ratio of the present invention. Electrostatic repulsion component C has insufficient density of electrostatic repulsion sites, failing to suppress particle attraction at high solids content; interfacial compatibility component D has scarce interfacial compatibility sites, failing to reduce the interfacial tension of the three phases. Neither component can effectively cooperate with the strong anchoring effect of the strong anchoring component B, resulting in a broken synergistic effect. In contrast, the present invention, through precise compounding ratios, ensures a match between the strengths of anchoring, electrostatic, and interfacial functions, achieving low viscosity and high stability at high solids content.

[0132] The dispersant prepared in Comparative Example 4, compared to the dispersant prepared in Example 4, uses a strongly dissociable sulfonate salt to replace the betaine-type sulfonyl group of the electrostatic repulsion component C of this invention, thus disrupting the ternary synergistic electrostatic equilibrium. This results in strong electrostatic interaction between the dispersant and the Mn group on the LMFP surface. 2+ The conflict triggers flocculation, interfering with the bimetallic chelate anchoring of the strongly anchoring component B-hydrazide and blocking the interfacial compatibility of the interfacial compatibility component D-sulfoxide, resulting in a negative cumulative effect. However, the mild electrostatic intramolecular charge balance design of this invention does not conflict with anchoring and interfacial functions, achieving a ternary synergistic adaptation of the LMFP bimetallic system.

[0133] The dispersant prepared in Comparative Example 5, compared to the dispersant prepared in Example 5, has a lower ≥90% grafting rate of the strong anchoring component B (oxazolidinone group) than the ≥90% required by this invention, resulting in weaker ternary synergistic anchoring support and lower Fe content on the LFP surface. 2+ High exposure levels and insufficient anchoring points make the dispersant prone to desorption, which in turn prevents the adhesion of the sulfonamide double layer of the electrostatic repulsion component C and the sulfoxide interfacial network of the interfacial compatibility component D, leading to the collapse of the synergistic system. In contrast, the high grafting rate design of this invention ensures dense anchoring points, providing a stable foundation for ternary synergy and meeting the adsorption requirements of low-carbon LFP.

[0134] Compared to the dispersant prepared in Example 6, the dispersant prepared in Comparative Example 6, by replacing the DMSO solvent and urea-formaldehyde polyether of the present invention, disrupts the ternary synergistic "interfacial bridge." NMP exhibits poor wettability to the high-carbon layer, and polyethylene glycol monomethyl ether lacks triple hydrogen bond sites, thus failing to effectively interact with the carbon layer. This leads to the failure of the interfacial compatibility function of component D, consequently affecting the anchoring function of strong anchoring component B and the electrostatic repulsion function of component C, resulting in the breakdown of the ternary synergy. In contrast, the synergistic design of DMSO and urea-formaldehyde groups in the present invention achieves dual interface optimization through solvent wetting and hydrogen bonding, providing a favorable interfacial environment for the ternary synergy and making it suitable for high-carbon LFP.

[0135] This invention also directly verifies the technical superiority of its dispersant by comparing it with three mainstream commercially available LFP dispersants. Performance data from the dispersants prepared in Comparative Examples 7-9 and the dispersant prepared in Example 1 show that, under the same solid content (68.3%) and the same addition amount (0.49%), the core performance of Example 1 is comprehensively superior to commercially available products. The core reason for the performance difference lies in the fact that commercially available dispersants generally lack the ternary synergistic design of "strong anchoring - stable electrostatics - superior interface".

[0136] Anchoring process: Commercially available dispersants mostly rely on traditional functional groups such as carboxyl groups and common amino groups, which interact with the Fe on the LFP surface. 2+ The dispersant forms only a single weak adsorption point, which easily leads to the desorption of the dispersant and secondary agglomeration of the particles; while the oxazolidinone group in Example 1 forms a six-membered coordination ring with Fe²⁺ through N and O atoms, which improves the adsorption strength by more than 30% compared with traditional functional groups, thus inhibiting agglomeration from the source.

[0137] Electrostatic aspect: Commercially available dispersants have two major problems. Either they are strong dissociative dispersants, which are prone to electrostatic adsorption with PVDF binders, leading to flocculation, with a viscosity rebound rate as high as 74.6% in 24 hours; or they have insufficient electrostatic repulsion, which cannot suppress particle attraction for a long time, with a rebound rate of 21.2%. In contrast, the sulfonamide group in Example 1 provides a mild and stable non-dissociative double layer with a stable zeta potential of 28~35mV, which avoids conflict with binders and can continuously suppress agglomeration.

[0138] Interface component: The interface components of commercially available dispersants are mostly simple ether groups, ester groups or alcohol hydroxyl groups, with polarity that is either too high or too low, which cannot match the three-phase polarity gradient of the carbon layer, binder and solvent on the LFP surface, resulting in high interfacial tension, poor compatibility and soaring viscosity at high solid content; while the sulfoxide group (medium polarity ε=30~35) in Example 1 acts as a "polar bridge", which can significantly reduce the three-phase interfacial tension, and at the same time form a stable interaction with each component, ensuring low viscosity and high stability at high solid content.

[0139] In summary, commercially available conventional dispersants, lacking a dedicated functional group design and ternary synergistic system, struggle to simultaneously achieve high solids content compatibility, low viscosity, and long-term stability. In contrast, this invention addresses the core pain points of commercially available products through the precise synergy of strong anchoring by the oxazolidinone group, electrostatic stability by the sulfonamide group, and superior interface by the sulfoxide group. Under the same application conditions, it exhibits superior process compatibility and performance reliability, giving it a strong competitive edge in the market.

[0140] 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.

[0141] 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.

[0142] 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 compound lithium iron phosphate dispersant, characterized in that, The compound lithium iron phosphate dispersant is composed of a strong anchoring component B, an electrostatic repulsion component C, and an interfacial compatibility component D; wherein... The strongly anchoring component B is a polymer with oxazolidinone and / or hydrazide groups, and has a number average molecular weight of 1000~8000 g / mol. The electrostatic repulsion component C is a polymer with sulfonamide groups and / or betaine-type sulfonyl groups, with a number average molecular weight of 800~6000 g / mol; The interface compatibility component D is a compound and / or polymer having sulfoxide groups and / or urea formate groups, with a number average molecular weight of 500~5000 g / mol.

2. The compounded lithium iron phosphate dispersant according to claim 1, characterized in that, The mass ratio of the strong anchoring component B, the electrostatic repulsion component C, and the interfacial compatibility component D in the compound lithium iron phosphate dispersant is 1:0.5~1.5:0.3~1.

3. The compound lithium iron phosphate dispersant according to claim 1 or 2, characterized in that, The grafting rate of oxazolidinone and / or hydrazide groups in the strongly anchoring component B is ≥90%; Preferably, the strongly anchoring component B is selected from one or more of oxazolidinone acrylate homopolymer, hydrazide methacrylate-styrene copolymer, and oxazolidinone modified polyether; Preferably, the electrostatic repulsion component C is selected from one or more of sulfonamide-modified vinyl ether homopolymers, betaine-type sulfoacrylamide copolymers, and sulfonamide-modified polyesters; The interface compatibility component D is selected from one or more of sulfoxide ethyl ether-grafted acrylic acid-NVP copolymer, sulfoxide propyl ether-grafted acrylic acid-NVP copolymer, and urethane polyether.

4. The compound lithium iron phosphate dispersant according to any one of claims 1-3, characterized in that, The compound lithium iron phosphate dispersant also contains solvent A, which is selected from one or more of N-methylpyrrolidone, deionized water and dimethyl sulfoxide; Solvent A accounts for 80-90% of the total mass of the compound lithium iron phosphate dispersant.

5. A method for preparing a compound lithium iron phosphate dispersant as described in any one of claims 1-4, characterized in that, The preparation method includes: 1) Mix the strong anchoring component B, the electrostatic repulsion component C, and the interfacial compatibility component D to obtain a mixture; Optionally, 2) add solvent A to the mixture obtained in step 1), and stir at 300-600 rpm for 30-60 min at a temperature of 25-60℃ to obtain a premixed system; 3) Stir the mixture from step 1) or the premixed system from step 2) at a temperature of 40~70℃ and a speed of 300~600rpm for 60~120min, and then cool to obtain the compound lithium iron phosphate dispersant.

6. The preparation method according to claim 5, characterized in that, In step 1), the mass ratio of the strong anchoring component B, the electrostatic repulsion component C, and the interfacial compatibility component D in the compound lithium iron phosphate dispersant is 1:0.5~1.5:0.3~1.0; The grafting rate of oxazolidinone and / or hydrazide groups in the strongly anchoring component B is ≥90%; Preferably, the strongly anchoring component B is selected from one or more of oxazolidinone acrylate homopolymer, hydrazide methacrylate-styrene copolymer, and oxazolidinone modified polyether; Preferably, the electrostatic repulsion component C is selected from one or more of sulfonamide-modified vinyl ether homopolymers, betaine-type sulfoacrylamide copolymers, and sulfonamide-modified polyesters; The interface compatibility component D is selected from one or more of sulfoxide ethyl ether, sulfoxide propyl ether, and urethane polyether.

7. The preparation method according to claim 5 or 6, characterized in that, In step 2), solvent A is selected from one or more of N-methylpyrrolidone, deionized water, and dimethyl sulfoxide; Solvent A accounts for 80-90% of the total mass of the dispersant.

8. The application of the compound lithium iron phosphate dispersant as described in any one of claims 1-4 in the preparation of lithium iron phosphate cathode slurry.

9. A lithium iron phosphate cathode slurry, characterized in that, The lithium iron phosphate cathode slurry, by weight, consists of the following components: 57-67 parts lithium iron phosphate base, 1-8 parts conductive agent, 1-5 parts binder, 0.06-2 parts dispersant, and 30-40 parts slurry solvent. The dispersant is the compound lithium iron phosphate dispersant as described in any one of claims 1 to 4; The lithium iron phosphate base material is selected from one or more of lithium iron phosphate, Mg-doped lithium iron phosphate, manganese iron phosphate, and carbon-coated lithium iron phosphate.

10. The lithium iron phosphate cathode slurry according to claim 9, characterized in that, The conductive agent is conductive carbon black and / or carbon nanotubes; The adhesive is selected from one or more of polyvinylidene fluoride, carboxymethyl hydroxyethyl cellulose, and polyvinyl alcohol; The solvent used for the slurry is selected from one or more of N-methylpyrrolidone, deionized water, and dimethyl sulfoxide; The lithium iron phosphate cathode slurry has a solid content of ≥60% and a viscosity of ≤10000 mPa·s.

Images