A method for preparing an ABA type triblock copolymer dispersant based on RAFT polymerization

Abstract

The application discloses a kind of ABA type three-block copolymer dispersant preparation methods based on RAFT polymerization, belong to the technical field of polymer material synthesis.The method includes: adding solvent N-methyl pyrrolidone, symmetric bifunctionality RAFT reagent, heterocyclic monomer E and long carbon chain acrylate monomer F to reactor, after nitrogen deoxygenation, temperature is raised to 100~140 ℃, and initiator I-1 is inputted dropwise N-vinyl pyrrolidone is reacted to obtain block A;Block A is formed by the copolymerization of N-vinyl pyrrolidone, heterocyclic monomer E and long carbon chain acrylate monomer F, and block B is formed by the copolymerization of unsaturated carboxylic acid monomer G and styrene, and the molecular weight distribution is 1.2~1.6.The dispersant is used for battery positive electrode slurry, and the content is 0.05%~0.4% of the weight of the positive electrode main material.The application realizes the controllable synthesis of ABA type three-block copolymer by one-step RAFT polymerization, and improves the dispersion stability of positive electrode slurry and the electrochemical performance of battery by precise design of molecular structure and optimization of compounding.

Description

Technical Field

[0001] This invention relates to the field of polymer material synthesis technology, and in particular to a method for preparing an ABA-type triblock copolymer dispersant based on RAFT polymerization. Background Technology

[0002] The dispersion stability of lithium-ion battery cathode slurry directly affects the battery's electrochemical performance and cycle life. Existing cathode slurry dispersants typically employ small-molecule dispersants or homopolymer dispersants. Small-molecule dispersants achieve particle dispersion through electrostatic repulsion, but in high-solids-content slurries, their steric hindrance effect is insufficient, resulting in poor dispersion stability. Homopolymer dispersants have a simple molecular structure, making it difficult to simultaneously achieve both anchoring effect on cathode active particles and compatibility with the dispersion medium, leading to large viscosity fluctuations and poor coating uniformity in the slurry.

[0003] Existing block copolymer dispersants are typically prepared using traditional free radical polymerization methods, resulting in a wide molecular weight distribution and poor controllability of the block structure. When the molecular weight distribution index is greater than 2.0, the low molecular weight components have insufficient dispersing ability, while the high molecular weight components are prone to forming micelles, leading to slurry flocculation, making it difficult to guarantee the performance consistency of the dispersant.

[0004] The synthesis of existing ABA-type triblock copolymers typically employs anionic polymerization or group transfer polymerization, which involves harsh reaction conditions, requiring extremely high monomer purity and an anhydrous and oxygen-free environment, resulting in high industrial production costs. While RAFT polymerization can achieve living radical polymerization, existing RAFT reagents are mostly monofunctional chain transfer reagents. The synthesis of ABA-type triblock copolymers requires multiple reaction steps and intermediate separation and purification, making the process complex and resulting in low product yields.

[0005] Existing dispersant molecular structure designs typically do not consider the specific application environment of cathode slurries. The surface of cathode active materials is mostly composed of metal oxides or phosphates, requiring dispersants to achieve anchoring through specific functional groups; cathode slurry solvents are usually N-methylpyrrolidone, necessitating good solvent compatibility in dispersants; and cathode slurries have high solids content and high shear rates, requiring dispersants to possess sufficient steric hindrance. Existing dispersants lack precise molecular structure design to address these requirements, resulting in insufficient dispersion efficiency.

[0006] The compatibility of existing dispersants with cathode slurries is generally not optimized. When dispersants are used alone, some polar groups interact too strongly with the surface of cathode particles, leading to slurry gelation. Insufficient dispersant dosage results in poor dispersion, while excessive dosage increases slurry viscosity and battery internal resistance. Existing methods do not adjust the polarity balance and rheological properties of dispersants by compounding small molecule compounds, resulting in insufficient adaptability of dispersants for application. Summary of the Invention

[0007] Therefore, embodiments of the present invention provide a method for preparing an ABA-type triblock copolymer dispersant based on RAFT polymerization. A method for preparing an ABA-type triblock copolymer dispersant based on RAFT polymerization is provided, comprising the following steps: Step 1, Synthesis of Block A: N-methylpyrrolidone solvent, RAFT reagent with symmetrical structure, heterocyclic monomer E and long carbon chain acrylate monomer F are added to the reactor. After stirring and dissolving, nitrogen gas is introduced to remove oxygen from the system. The temperature is raised to 100~140℃ under nitrogen atmosphere, initiator I-1 is added, and then N-vinylpyrrolidone is added dropwise over a period of 5~10 hours. After the addition is completed, the reaction is maintained at the temperature for 2 hours to obtain block A. Step 2, Synthesis of Block B: The product obtained in Step 1 is cooled to 50~80℃, initiator I-2 is added, and unsaturated carboxylic acid monomer G, styrene and solvent N-methylpyrrolidone are added in one go. After reacting at this temperature for 6~24h, the unreacted monomers are removed by vacuuming for 1h while maintaining the temperature, and ABA-type triblock copolymer C is obtained. The number average molecular weight of the ABA-type triblock copolymer C is 15,000~100,000 and the molecular weight distribution is 1.2~1.6. Step 3, formulation of dispersant: The ABA-type triblock copolymer C obtained in step 2 and the carboxyl-containing small molecule compound D are added to the solvent N-methylpyrrolidone, heated to 40~50℃ and stirred to dissolve, and then vacuum dehydrated at this temperature to obtain the ABA-type triblock copolymer dispersant; In the dispersant, ABA-type triblock copolymer C accounts for 80-95 wt%, carboxyl-containing small molecule compound D accounts for 5-20 wt%, and the solid content of the dispersant is 30-50 wt%. Beneficial effects

[0008] The beneficial effects of the technical solutions provided in the embodiments of the present invention include at least the following: This invention utilizes a bifunctional RAFT reagent with a symmetrical structure to copolymerize block A with N-vinylpyrrolidone, heterocyclic monomer E, and long-chain acrylate monomer F, and block B with unsaturated carboxylic acid monomer G, styrene, and other monomers, thus obtaining ABA-type triblock copolymer C in a one-step process. This solves the technical problems of existing technologies that require multiple steps and intermediate separation and purification to synthesize ABA-type triblock copolymers using monofunctional RAFT reagents, resulting in complex processes and low product yields. The invention achieves the technical effect of synthesizing ABA-type triblock copolymers in a one-step process using a symmetrical bifunctional RAFT reagent, simplifying the process and improving product yield and structural controllability.

[0009] This invention addresses the technical problem in existing technologies where the dispersant molecular structure does not simultaneously consider anchoring effect and solvent compatibility. It achieves the technical effect of improving the dispersion stability of the positive electrode slurry through a synergistic design that utilizes N-vinylpyrrolidone to provide solvent compatibility, heterocyclic monomer E to provide polar anchoring sites, and long-chain acrylate monomer F to provide steric hindrance effect. Block A is copolymerized from N-vinylpyrrolidone, heterocyclic monomer E, and long-chain acrylate monomer F. The mass fractions of these three monomers in the total mass of block A are 70%–89%, 8%–20%, and 3%–10%, respectively. The total mass of block A accounts for 70–90 wt% of the total mass of the ABA-type triblock copolymer C.

[0010] This invention addresses the technical problems of wide molecular weight distribution, insufficient dispersion of low molecular weight components, and easy flocculation of high molecular weight components in traditional free radical polymerization by controlling the comonomers of block B to include unsaturated carboxylic acid monomer G, styrene, acrylate monomer H, and acrylonitrile. Block B accounts for 10-30 wt% of the total mass of ABA-type triblock copolymer C, and the number average molecular weight of block B is 15,000-100,000, with a molecular weight distribution of 1.2-1.6. It achieves the technical effect of controlling a narrow molecular weight distribution through RAFT living polymerization, providing a supporting skeleton through the rigid segments of block B, and adjusting the overall polarity balance of the dispersant. Attached Figure Description

[0011] Figure 1 Slurry viscosity comparison chart; Figure 2 A flowchart provided for an embodiment of this application.

[0012] Figure 3 Here are the structural formulas of RAFT reagent a, RAFT reagent b, and RAFT reagent c. Detailed Implementation

[0013] To make the technical problems, technical solutions and advantages of the present invention clearer, a detailed description will be given below in conjunction with the accompanying drawings and specific embodiments.

[0014] like Figure 2 As shown, a method for preparing an ABA-type triblock copolymer dispersant based on RAFT polymerization includes the following steps: Step 1, Synthesis of Block A: N-methylpyrrolidone solvent, RAFT reagent with symmetrical structure, heterocyclic monomer E and long carbon chain acrylate monomer F are added to the reactor. After stirring and dissolving, nitrogen gas is introduced to remove oxygen from the system. The temperature is raised to 100~140℃ under nitrogen atmosphere, initiator I-1 is added, and then N-vinylpyrrolidone is added dropwise over a period of 5~10 hours. After the addition is completed, the reaction is maintained at the temperature for 2 hours to obtain block A. Step 2, Synthesis of Block B: The product obtained in Step 1 is cooled to 50~80℃, initiator I-2 is added, and unsaturated carboxylic acid monomer G, styrene and solvent N-methylpyrrolidone are added in one go. After reacting at this temperature for 6~24h, the unreacted monomers are removed by vacuuming for 1h while maintaining the temperature, and ABA-type triblock copolymer C is obtained. The number average molecular weight of the ABA-type triblock copolymer C is 15,000~100,000 and the molecular weight distribution is 1.2~1.6. Step 3, formulation of dispersant: The ABA-type triblock copolymer C obtained in step 2 and the carboxyl-containing small molecule compound D are added to the solvent N-methylpyrrolidone, heated to 40~50℃ and stirred to dissolve, and then vacuum dehydrated at this temperature to obtain the ABA-type triblock copolymer dispersant; In the dispersant, ABA-type triblock copolymer C accounts for 80-95 wt%, carboxyl-containing small molecule compound D accounts for 5-20 wt%, and the solid content of the dispersant is 30-50 wt%.

[0015] It should be noted that: Step 1 uses a RAFT reagent with a symmetrical structure. The leaving groups at both ends of the reagent have the same structure. During polymerization, the two active chains grow synchronously from the molecular center to both ends. After the polymerization of block A monomer is completed, block B monomer is added at once. The two-step feeding can obtain an ABA-type triblock structure with the two blocks A having the same structure and block B in the middle. N-vinylpyrrolidone is added dropwise, accounting for 70% to 89% of the total mass of block A monomer. A one-time addition will cause the system to polymerize rapidly and the molecular weight distribution to become uncontrollable. The dropwise addition time of 5 to 10 hours is derived from the examples. Example 1 was added for 5 hours, Example 2 for 10 hours, and Example 3 for 8 hours. The dropwise addition time corresponds to the total amount of monomer added and the reaction temperature. After the dropwise addition is completed, the temperature is maintained for 2 hours to ensure that the residual monomer is completely converted. The reason for cooling to 50~80℃ in step two is that the unsaturated carboxylic acid monomer contained in block B is prone to chain transfer side reactions above 100℃. After cooling, a medium-low temperature initiator is added and the holding time is 6~24h. Example 2 is held for 6h, and Examples 1 and 3 are held for 12h. After the holding is completed, the temperature is maintained and vacuum is applied for 1h to remove unreacted monomers. In step two, unsaturated carboxylic acid monomer G and styrene are essential monomers for block B. Acrylate monomer H and acrylonitrile can be omitted. Even without acrylate monomer H and acrylonitrile, the resulting dispersant still has dispersing ability. The only difference is that the viscosity of the slurry fluctuates more between different suppliers' main materials than the scheme using both. The two are used to adjust the polarity of block B to adapt to different cathode main materials. Number average molecular weight and molecular weight distribution were determined by gel permeation chromatography. The gel column was an Agilent PLgel 5 μm MIXED-C, the column temperature was 55 °C, the mobile phase was N-methylpyrrolidone, the flow rate was 1.0 mL / min, and the detection was performed using a differential refractive index detector. PMMA standard sample was used for calibration. The number average molecular weight of Example 2 was 15,000, which was at the lower limit of the range, and the number average molecular weight of Example 3 was 97,300, which was at the upper limit of the range. The molecular weight distributions of Examples 1 to 3 were 1.35, 1.44 and 1.46, respectively, all within the range of 1.2 to 1.6. Comparative Example 1 used the exact same monomer composition as Example 1, without the addition of RAFT reagent for ordinary free radical polymerization, and the product had a molecular weight distribution of 2.34. It directly gelled in a slurry with a solid content of 66%. Only copolymers with a narrow molecular weight distribution and a triblock structure can play a dispersing role at this solid content. In step three, the solid contents measured in Examples 1 to 3 were 30.1%, 40.1%, and 30.2%, respectively, all within the range of 30-50 wt%. The basis for the ABA-type triblock copolymer C accounting for 80-95 wt% and the carboxyl-containing small molecule compound D accounting for 5-20 wt% was Comparative Example 2. In Comparative Example 2, the viscosity rebound of the slurry after 48 hours was 89.1% when no small molecule compound D was added. In Examples 1 to 3, the viscosity rebound after 48 hours was no greater than 15.0% after the addition of small molecule compound D.

[0016] As an optional embodiment, block A is copolymerized from three monomers: N-vinylpyrrolidone, heterocyclic monomer E, and long-chain acrylate monomer F, with the three monomers accounting for 70%–89%, 8%–20%, and 3%–10% of the total mass of block A monomers, respectively. The comonomers of block B include unsaturated carboxylic acid monomer G, styrene, acrylate monomer H, and acrylonitrile, with the four monomers accounting for 40%–95%, 5%–10%, 0–20%, and 0–40% of the total mass of block B monomers, respectively. The total mass of block A accounts for 70-90 wt% of the total mass of ABA-type triblock copolymer C, and block B accounts for 10-30 wt%.

[0017] It should be noted that: The mass fraction of each monomer is calculated by dividing the mass of a single monomer by the total mass of the monomers in the block. A mass fraction of 0 indicates that the monomer does not participate in copolymerization. Taking Example 1 as an example, the total mass of block A monomers is 59.5 + 28 + 262.5 = 350 g, the proportion of N-vinylpyrrolidone is 262.5 / 350 = 75%, the proportion of heterocyclic monomer E is 59.5 / 350 = 17%, and the proportion of long-chain acrylate monomer F is 28 / 350 = 8%. The total mass of block B monomers is 120 + 15 + 7.5 + 7.5 = 150 g. The proportion of unsaturated carboxylic acid monomer G is 120 / 150 = 80%, styrene is 15 / 150 = 10%, acrylonitrile is 7.5 / 150 = 5%, and acrylate monomer H is 7.5 / 150 = 5%. Block A accounts for 70 wt% of the total copolymer mass (350 / (350+150) = 70 wt%), while in Example 3, the proportion of block A is approximately 84.9 wt% (450 / (450+80)). The lower limit of the mass fraction of acrylate monomer H and acrylonitrile is 0, meaning that the two can not participate in copolymerization. The dispersant obtained without adding the two still has dispersing ability, only the viscosity of the slurry fluctuates more between different suppliers of main materials. Adding the two can adjust the polarity of block B to adapt to different positive electrode main materials.

[0018] As an optional embodiment, the heterocyclic monomer E is a polymerizable monomer containing a five-membered or six-membered heterocycle, selected from one or more of 4-acryloylmorpholine, 2-vinylpyridine, 4-vinylpyridine, and acetone glyceryl acrylate in any proportion.

[0019] It should be noted that: Of the four heterocyclic monomers, 4-acryloylmorpholine was used in Example 1, acetone glyceryl acrylate was used in Example 2, and 4-vinylpyridine was used in Example 3. The molecular weight distribution of the copolymers obtained in each example was between 1.2 and 1.6. The heterocyclic structures are determined as follows: 4-acryloylmorpholine contains a six-membered morpholine ring, 2-vinylpyridine and 4-vinylpyridine contain a six-membered pyridine ring, and acetone glyceryl acrylate contains a five-membered dioxolane ring. The nitrogen- or oxygen-containing heterocyclic structures in heterocyclic monomer E have a good affinity for the solvent N-methylpyrrolidone and can form a solvation layer. The steric hindrance of the cyclic structure is greater than that of the linear segment, and together with the long carbon chain acrylate monomer F, they constitute the steric hindrance structure of block A.

[0020] As an optional embodiment, the structure of the long-chain acrylate monomer F is as follows:

[0021] in, -H or - , for alkyl chain.

[0022] It should be noted that: The carbon chain lengths of C4 to C12 are derived from the monomers used in the examples. The ester group of n-butyl acrylate used in Example 1 and tert-butyl acrylate used in Example 2 has 4 carbons, and the ester group of lauryl methacrylate used in Example 3 has 12 carbons. When -H, it corresponds to an acrylate monomer. for- This corresponds to methacrylate monomers; When the number of carbon atoms in the ester-alkyl chain is less than 4, the chain segment flexibility is insufficient. When the number of carbon atoms is greater than 12, the compatibility with the solvent N-methylpyrrolidone decreases, and block A cannot fully expand in the solvent to form a solvation layer.

[0023] As an optional embodiment, the unsaturated carboxylic acid monomer G is selected from one or more of acrylic acid, methacrylic acid, maleic anhydride, maleic acid, fumaric acid, and itaconic acid, mixed in any proportion; The acrylate monomer H is an acrylate or methacrylate with 1 to 4 carbon atoms in the ester group, selected from methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, n-propyl acrylate, n-propyl methacrylate, isopropyl acrylate, isopropyl methacrylate, n-butyl acrylate, n-butyl methacrylate, isobutyl acrylate, isobutyl methacrylate, tert-butyl acrylate, and tert-butyl methacrylate, mixed in any proportion.

[0024] It should be noted that: In the unsaturated carboxylic acid monomer G, acrylic acid was used in Examples 1 and 2, and a mixture of acrylic acid and itaconic acid was used in Example 3; The number of carbon atoms in the ester group of acrylate monomer H was determined as follows: methyl ester has 1 carbon atom, ethyl ester has 2 carbon atom, n-propyl ester and isopropyl ester have 3 carbon atom, and n-butyl ester, isobutyl ester and tert-butyl ester have 4 carbon atom. In the acrylate monomer H, methyl acrylate was used in Example 1, ethyl acrylate was used in Example 2, and tert-butyl acrylate was used in Example 3; The carboxyl group provided by the unsaturated carboxylic acid monomer G is the anchoring site for the adsorption of block B on the surface of the cathode material particles. The benzene ring of styrene and the ester group of acrylate monomer H are used to adjust the polarity of block B, so that block B can adapt to the surface properties of different cathode materials.

[0025] As an optional embodiment, the RAFT reagent is a bifunctional chain transfer reagent with the same leaving groups at both ends, and its amount accounts for 0.3 to 2.5 wt% of the total mass of the three monomers: heterocyclic monomer E, long-chain acrylate monomer F, and N-vinylpyrrolidone.

[0026] It should be noted that: The amount of RAFT reagent used is calculated by dividing the mass of RAFT reagent by the sum of the masses of the heterocyclic monomer E, the long-chain acrylate monomer F, and the N-vinylpyrrolidone. For example, in Example 1, the content is 7 / 350 = 2.0 wt%; in Example 2, it is 10 / 400 = 2.5 wt%; and in Example 3, it is 1.8 / 450 = 0.4 wt%. The amount of RAFT reagent used determines the number of active chains in the system. The lower the amount, the higher the molecular weight of the product. In Example 2, the amount of 2.5 wt% corresponds to a number average molecular weight of 15,000, and in Example 3, the amount of 0.4 wt% corresponds to a number average molecular weight of 97,300. Bifunctional chain transfer reagents with the same leaving groups at both ends form two active chains with the same structure during polymerization, and ABA-type triblock copolymers can be obtained in two feeding steps. RAFT reagents with different leaving groups require three feeding steps to obtain the same block structure.

[0027] As an optional embodiment, the initiator I-1 is selected from one of di-tert-butyl peroxide, tert-butyl peroxyisopropyl carbonate, tert-butyl peroxyacetate, tert-butyl peroxybenzoate, and dicumyl peroxide; The molar ratio of initiator I-1 to RAFT reagent is 1:8~20.

[0028] It should be noted that: The molar ratio is calculated by dividing the mass of each substance by its molar mass to obtain the amount of substance, and then calculating the ratio between the two. The extreme values ​​and the middle values ​​of the molar ratio of 1:8 to 20 correspond to 1:8 in Example 3, 1:10 in Example 1, and 1:20 in Example 2, respectively. In RAFT polymerization, the concentration of active chains is determined by the RAFT reagent. The initiator is only used to start the polymerization. When the molar ratio is higher than 1:8, the proportion of dead chains directly initiated by primary free radicals increases and the molecular weight distribution becomes wider. When the molar ratio is lower than 1:20, the free radical flux is insufficient and the monomer conversion rate decreases. Initiator I-1 is a high-temperature peroxide initiator, whose half-life temperature matches the reaction temperature of 100~140℃ in step one.

[0029] As an optional embodiment, the initiator I-2 is selected from one of azobisisobutyronitrile, azobisisoheptanenitrile, benzoyl peroxide, lauroyl peroxide, and diethylhexyl peroxide. The molar ratio of initiator I-2 to RAFT reagent is 1:3~10.

[0030] It should be noted that: The extreme values ​​and the middle values ​​of the molar ratio of 1:3 to 10 correspond to 1:3 in Example 2, 1:5 in Example 1, and 1:6 in Example 3, respectively. The amount of initiator I-2 used is higher than that of RAFT reagent because step two is a one-time feeding and the reaction temperature is reduced to 50~80℃, requiring more free radicals to ensure that the block B monomer is fully polymerized within 6~24h. Initiator I-2 is selected from azo initiators or medium-low temperature peroxide initiators, and its half-life temperature matches the reaction temperature of 50~80℃ in step two.

[0031] As an optional embodiment, the ABA-type triblock copolymer dispersant is added during the preparation of the battery cathode slurry, and the dosage is 0.05% to 0.4% of the weight of the cathode material, wherein the dosage is the folded solid dosage.

[0032] It should be noted that: The dosing range is derived from the lithium iron phosphate slurry formulation in the slurry preparation and viscosity testing method, which has a main material: binder: conductive agent: dispersant ratio of 97.1:2:0.7:0.2, and the dispersant dosage is 0.2% of the weight of the positive electrode main material, which is within the range of 0.05% to 0.4%. When the dosage is less than 0.05%, the dispersant is insufficient to cover the surface of the main material particles, resulting in poor consolidation and adhesion stabilization performance. When the dosage is higher than 0.4%, the dispersing performance no longer increases with the dosage, and further increasing the dosage will result in waste of raw materials.

[0033] As an optional embodiment, the molecule of the carboxyl-containing small molecule compound D contains a hydroxyl group or another carboxyl group in addition to the carboxyl group, selected from one or more of oxalic acid, malonic acid, succinic acid, adipic acid, salicylic acid, p-hydroxybenzoic acid, lactic acid, dihydroxybenzoic acid, citric acid, tartaric acid, and phthalic acid in any proportion.

[0034] It should be noted that: The small molecule compound D containing a carboxyl group corresponds to oxalic acid in Example 1, salicylic acid in Example 2, and phthalic acid in Example 3, respectively; The common structural characteristics are as follows: oxalic acid, malonic acid, succinic acid, adipic acid, citric acid, tartaric acid, and phthalic acid contain two or more carboxyl groups; salicylic acid, p-hydroxybenzoic acid, and dihydroxybenzoic acid contain carboxyl groups and phenolic hydroxyl groups; lactic acid contains carboxyl groups and hydroxyl groups; and the total number of polar groups in each of the eleven compounds is not less than two. The action pathway of small molecule compound D is as follows: ABA-type triblock copolymer C first adsorbs onto the surface of the main material particles to form an anchoring layer, and then small molecule compound D slowly adsorbs onto the particle surface area not covered by copolymer C. The two form a relay adsorption, which keeps the slurry viscosity stable for a long time. Comparative Example 2 showed normal initial dispersion without the addition of small molecule compound D, but the viscosity rebounded by 89.1% after 48 hours. When the amount of small molecule compound D was less than 5 wt%, the auxiliary stabilizing effect was insufficient, and when it was more than 20 wt%, the proportion of the main dispersing component decreased, and the initial dispersion performance deteriorated. Example

[0035] I. Testing Methods 1. Molecular weight and molecular weight distribution test The number-average molecular weight and molecular weight distribution of the copolymers were determined by gel permeation chromatography using a Waters 1515 gel permeation chromatograph with an Agilent PLgel 5 μm MIXED-C column at 55 °C. The mobile phase was N-methylpyrrolidone at a flow rate of 1.0 mL / min, and the detector was a Waters 2414 differential refractive index detector. The molecular weight standard was a PMMA-type GPC standard.

[0036] 2. Slurry preparation and viscosity testing The slurry was prepared according to the mass ratio of lithium iron phosphate main material: PVDF: conductive agent SP: dispersant = 97.1:2:0.7:0.2. The dispersant was added as solids, accounting for 0.2% of the weight of the positive electrode main material. N-methylpyrrolidone solvent was added to make the solid content of the slurry 66%. After homogenizing in a vacuum degassing machine for 4 hours, the viscosity of the discharged material was measured. Then the slurry was allowed to stand at room temperature, and the viscosity of the slurry after standing for 24 hours and 48 hours was measured respectively. The percentage increase of viscosity after 48 hours relative to the discharge viscosity was calculated.

[0037] 3. Raw Material Description In the following examples, RAFT reagent a, RAFT reagent b, and RAFT reagent c are all symmetrical bifunctional chain transfer reagents with the same leaving groups at both ends, and their structural formulas are shown in the attached figures of the specification.

[0038] II. Example 1 Step 1, Synthesis of Block A: 350g of N-methylpyrrolidone, 7g of RAFT reagent a, 59.5g of 4-acryloylmorpholine, and 28g of n-butyl acrylate were added to a reactor equipped with a stirrer, thermometer, nitrogen tube, and reflux condenser. After stirring and dissolving, nitrogen gas was introduced for 30 minutes to remove oxygen from the system. The temperature was raised to 100℃ under a nitrogen atmosphere, and 0.437g of tert-butyl peroxyisopropyl carbonate initiator was added. The molar ratio of tert-butyl peroxyisopropyl carbonate to RAFT reagent a was 1:10. Subsequently, 262.5g of N-vinylpyrrolidone was added dropwise over 5 hours. After the addition was completed, the reaction was maintained at this temperature for 2 hours to obtain block A. Step 2, Synthesis of Block B: The product obtained in Step 1 was cooled to 52°C and added in one go to a mixed solution consisting of 120g acrylic acid, 15g styrene, 7.5g acrylonitrile, 7.5g methyl acrylate and 150g N-methylpyrrolidone solvent. 1.723g of initiator diethylhexyl peroxide was added, with a molar ratio of 1:5 to RAFT reagent a. After reacting at this temperature for 12h, the unreacted monomers were removed by vacuuming for 1h, yielding ABA-type triblock copolymer C. The number-average molecular weight was 24,500 and the molecular weight distribution was 1.35, as determined by GPC. Step 3, preparation of the dispersant: Add 459g of N-methylpyrrolidone, 510g of the ABA-type triblock copolymer obtained in Step 2, and 15g of oxalic acid to a reaction flask equipped with a mechanical stirrer. Heat to 40-50℃ and stir to dissolve. Then, dehydrate under vacuum at this temperature to obtain the dispersant, and determine that the solid content is 30.1%. According to the above-mentioned slurry preparation and viscosity testing methods, the slurry output viscosity is 5220 cp, the viscosity after standing for 24 hours is 5385 cp, the viscosity after standing for 48 hours is 5722 cp, and the viscosity increase percentage after 48 hours is 9.6%.

[0039] III. Example 2 Step 1, Synthesis of Block A: 600g of N-methylpyrrolidone, 10g of RAFT reagent b, 40g of acetone glyceryl acrylate, and 20g of tert-butyl acrylate were added to a reactor equipped with a stirrer, thermometer, nitrogen tube, and reflux condenser. After stirring and dissolving, nitrogen gas was introduced for 30 min to remove oxygen from the system. The temperature was raised to 120℃ under a nitrogen atmosphere, and 0.597g of dicumyl peroxide initiator was added. The molar ratio of dicumyl peroxide to RAFT reagent b was 1:20. Then, 340g of N-vinylpyrrolidone was added dropwise over 10 h. After the addition was completed, the reaction was maintained at the temperature for 2 h to obtain block A. Step 2, Synthesis of Block B: The product obtained in Step 1 was cooled to 70°C and added in one go to a mixed solution consisting of 45g acrylic acid, 15g styrene, 20g acrylonitrile, 20g ethyl acrylate and 150g N-methylpyrrolidone solvent. 2.419g of initiator azobisisobutyronitrile was added, with a molar ratio of 1:3 to RAFT reagent b. After reacting at this temperature for 6 hours, the unreacted monomers were removed by vacuuming for 1 hour while maintaining the temperature, resulting in ABA-type triblock copolymer C. The number average molecular weight was 15,000 and the molecular weight distribution was 1.44, as determined by GPC. Step 3, preparation of the dispersant: Add 120g of N-methylpyrrolidone, 808g of the ABA-type triblock copolymer obtained in Step 2, and 18g of salicylic acid to a reaction flask equipped with a mechanical stirrer. Heat to 40-50℃ and stir to dissolve. Then, dehydrate under vacuum at this temperature to obtain the dispersant, and determine that the solid content is 40.1%. According to the above-mentioned slurry preparation and viscosity testing methods, the slurry output viscosity was 5252 cp, the viscosity after standing for 24 hours was 5486 cp, the viscosity after standing for 48 hours was 5975 cp, and the viscosity increase percentage after 48 hours was 13.8%.

[0040] IV. Example 3 Step 1, Synthesis of Block A: 800g of N-methylpyrrolidone, 1.8g of RAFT reagent c, 58.5g of 4-vinylpyridine, and 31.5g of lauryl methacrylate were added to a reactor equipped with a stirrer, thermometer, nitrogen tube, and reflux condenser. After stirring and dissolving, nitrogen gas was introduced for 30 min to remove oxygen from the system. The temperature was raised to 130℃ under a nitrogen atmosphere, and 0.118g of di-tert-butyl peroxide initiator was added. The molar ratio of di-tert-butyl peroxide to RAFT reagent c was 1:8. Then, 360g of N-vinylpyrrolidone was added dropwise over 8 h. After the addition was completed, the reaction was maintained at the temperature for 2 h to obtain block A. Step 2, Synthesis of Block B: The product obtained in Step 1 was cooled to 80°C and added in one go to a mixed solution consisting of 50g acrylic acid, 10g itaconic acid, 7.5g styrene, 10.5g acrylonitrile, 2g tert-butyl acrylate and 300g N-methylpyrrolidone solvent. 0.261g of benzoyl peroxide initiator was added, with a molar ratio of benzoyl peroxide to RAFT reagent c of 1:6. After reacting at this temperature for 12h, the unreacted monomers were removed by vacuuming for 1h, yielding ABA-type triblock copolymer C. The number-average molecular weight was 97,300 and the molecular weight distribution was 1.46, as determined by GPC. Step 3, preparation of the dispersant: Add 125g of N-methylpyrrolidone, 845g of the ABA-type triblock copolymer obtained in step 2, and 12g of phthalic acid to a reaction flask equipped with a mechanical stirrer. Heat to 40-50℃ and stir to dissolve. Then, dehydrate under vacuum at this temperature to obtain the dispersant, and determine that the solid content is 30.2%. According to the above slurry preparation and viscosity testing methods, the viscosity of the slurry output was 5176 cp, the viscosity after standing for 24 hours was 5421 cp, the viscosity after standing for 48 hours was 5952 cp, and the viscosity increase percentage after 48 hours was 15.0%.

[0041] V. Comparative Example 1 The monomer composition used in Comparative Example 1 is exactly the same as that in Example 1. The difference is that no RAFT reagent is added, and ordinary free radical polymerization is used. The product is a random copolymer, which is a non-ABA triblock copolymer. The specific process is as follows.

[0042] 500g of N-methylpyrrolidone solvent was added to a reactor equipped with a stirrer, thermometer, nitrogen tube, and reflux condenser. Nitrogen gas was introduced for 30 min to remove oxygen from the system. The temperature was raised to 100℃, and 0.437g of tert-butyl peroxyisopropyl carbonate initiator was added. Subsequently, a mixed solution consisting of 59.5g of 4-acryloylmorpholine, 28g of n-butyl acrylate, 262.5g of N-vinylpyrrolidone, 120g of acrylic acid, 15g of styrene, 7.5g of acrylonitrile, and 7.5g of methyl acrylate was added dropwise over a period of 5 h. After the addition was completed, the reaction was maintained at the temperature for 10 h. The temperature was lowered to 50℃, and a vacuum was applied for 1 h to remove unreacted monomers, yielding a random copolymer. The number average molecular weight was 47,500 and the molecular weight distribution was 2.34, as determined by GPC. 459g of N-methylpyrrolidone, 510g of random copolymer and 15g of oxalic acid were added to a reaction flask equipped with a mechanical stirrer. The mixture was heated to 40-50℃ and stirred to dissolve. Then, the mixture was dehydrated under vacuum at this temperature, and the solid content was determined to be 30.1%. The slurry was prepared according to the above slurry preparation and viscosity testing method. The slurry gelled directly at a solid content of 66%, and the viscosity could not be measured.

[0043] VI. Comparative Example 2 The difference between Comparative Example 2 and Example 1 is that a small molecule compound D containing a carboxyl group is not added in step three. The specific process is as follows.

[0044] 459g of N-methylpyrrolidone and 510g of the ABA-type triblock copolymer obtained in step 2 of Example 1 were added to a reaction flask equipped with a mechanical stirrer. The mixture was heated to 40-50°C and stirred until homogeneous. Then, the mixture was dehydrated under vacuum at this temperature to obtain a dispersant. According to the above-mentioned slurry preparation and viscosity testing methods, the slurry output viscosity was 4117 cp, the viscosity after standing for 24 hours was 5816 cp, the viscosity after standing for 48 hours was 7785 cp, and the viscosity increase percentage after 48 hours was 89.1%.

[0045] VII. Effect Verification The slurry viscosity test results of Examples 1 to 3, Comparative Example 1 and Comparative Example 2 are shown in Table 1 and 2. Figure 1 .

[0046] Table 1. Results of slurry viscosity test From Table 1 and Figure 1It can be seen that the dispersants obtained in Examples 1 to 3 can keep the lithium iron phosphate slurry in a flowable state at a solid content of 66%, with an output viscosity of 5176~5252cp and a viscosity increase percentage of 9.6%~15.0% after 48 hours, and the slurry viscosity remains stable within 48 hours. The copolymer composition of Comparative Example 1 is the same as that of Example 1, but RAFT polymerization was not used. The product is a random copolymer with a molecular weight distribution of 2.34. Its slurry gels directly at a solid content of 66%, and the viscosity cannot be measured. This indicates that only copolymers with a narrow molecular weight distribution and an ABA-type triblock structure can keep the slurry dispersed stably at this solid content. The difference between Comparative Example 2 and Example 1 is that the small molecule compound D is not added. Its slurry output viscosity is 4117cp, but the viscosity increase percentage after 48 hours reaches 89.1%, indicating that the small molecule compound D plays an important role in suppressing the viscosity rebound of the slurry.

[0047] Obviously, those skilled in the art can make various modifications and variations to this application without departing from the scope of this application. Therefore, if such modifications and variations fall within the scope of the claims of this application and their equivalents, this application also intends to include such modifications and variations.

Claims

1. A method for preparing an ABA-type triblock copolymer dispersant based on RAFT polymerization, characterized in that, Includes the following steps: Step 1, Synthesis of Block A: N-methylpyrrolidone solvent, RAFT reagent with symmetrical structure, heterocyclic monomer E and long carbon chain acrylate monomer F are added to the reactor. After stirring and dissolving, nitrogen gas is introduced to remove oxygen from the system. The temperature is raised to 100~140℃ under nitrogen atmosphere, initiator I-1 is added, and then N-vinylpyrrolidone is added dropwise over a period of 5~10 hours. After the addition is completed, the reaction is maintained at the temperature for 2 hours to obtain block A. Step 2, Synthesis of Block B: The product obtained in Step 1 is cooled to 50~80℃, initiator I-2 is added, and unsaturated carboxylic acid monomer G, styrene and solvent N-methylpyrrolidone are added in one go. After reacting at this temperature for 6~24h, the unreacted monomers are removed by vacuuming for 1h while maintaining the temperature, and ABA-type triblock copolymer C is obtained. The number average molecular weight of the ABA-type triblock copolymer C is 15,000~100,000 and the molecular weight distribution is 1.2~1.

6. Step 3, formulation of dispersant: The ABA-type triblock copolymer C obtained in step 2 and the carboxyl-containing small molecule compound D are added to the solvent N-methylpyrrolidone, heated to 40~50℃ and stirred to dissolve, and then vacuum dehydrated at this temperature to obtain the ABA-type triblock copolymer dispersant; In the dispersant, ABA-type triblock copolymer C accounts for 80-95 wt%, carboxyl-containing small molecule compound D accounts for 5-20 wt%, and the solid content of the dispersant is 30-50 wt%.

2. The preparation method according to claim 1, characterized in that, Block A is copolymerized from three monomers: N-vinylpyrrolidone, heterocyclic monomer E, and long-chain acrylate monomer F. The mass fractions of the three monomers in the total mass of block A are 70%–89%, 8%–20%, and 3%–10%, respectively. The comonomers of block B include unsaturated carboxylic acid monomer G, styrene, acrylate monomer H, and acrylonitrile, with the four monomers accounting for 40%–95%, 5%–10%, 0–20%, and 0–40% of the total mass of block B monomers, respectively. The total mass of block A accounts for 70-90 wt% of the total mass of ABA-type triblock copolymer C, and block B accounts for 10-30 wt%.

3. The preparation method according to claim 2, characterized in that, The heterocyclic monomer E is a polymerizable monomer containing a five-membered or six-membered heterocycle, selected from one or more of 4-acryloylmorpholine, 2-vinylpyridine, 4-vinylpyridine, and acetone glyceryl acrylate in any proportion.

4. The preparation method according to claim 3, characterized in that, The structure of the long-chain acrylate monomer F is as follows: ； in, -H or - , for alkyl chain.

5. The preparation method according to claim 4, characterized in that, The unsaturated carboxylic acid monomer G is selected from one or more of acrylic acid, methacrylic acid, maleic anhydride, maleic acid, fumaric acid, and itaconic acid, mixed in any proportion. The acrylate monomer H is an acrylate or methacrylate with 1 to 4 carbon atoms in the ester group, selected from methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, n-propyl acrylate, n-propyl methacrylate, isopropyl acrylate, isopropyl methacrylate, n-butyl acrylate, n-butyl methacrylate, isobutyl acrylate, isobutyl methacrylate, tert-butyl acrylate, and tert-butyl methacrylate, mixed in any proportion.

6. The preparation method according to claim 5, characterized in that, The RAFT reagent is a bifunctional chain transfer reagent with the same leaving groups at both ends, and its amount accounts for 0.3 to 2.5 wt% of the total mass of the three monomers: heterocyclic monomer E, long-chain acrylate monomer F, and N-vinylpyrrolidone.

7. The preparation method according to claim 6, characterized in that, The initiator I-1 is selected from one of di-tert-butyl peroxide, tert-butyl peroxyisopropyl carbonate, tert-butyl peroxyacetate, tert-butyl peroxybenzoate, and dicumyl peroxide. The molar ratio of initiator I-1 to RAFT reagent is 1:8~20.

8. The preparation method according to claim 7, characterized in that, The initiator I-2 is selected from one of azobisisobutyronitrile, azobisisoheptanenitrile, benzoyl peroxide, lauroyl peroxide, and diethylhexyl percarbonate. The molar ratio of initiator I-2 to RAFT reagent is 1:3~10.

9. The preparation method according to claim 8, characterized in that, The ABA-type triblock copolymer dispersant is added during the preparation of the battery cathode slurry, and the dosage is 0.05% to 0.4% of the weight of the cathode material, wherein the dosage is the folded solid dosage.

10. The preparation method according to claim 9, characterized in that, The molecule of the carboxyl-containing small molecule compound D contains a hydroxyl group or another carboxyl group in addition to the carboxyl group, and is selected from one or more of oxalic acid, malonic acid, succinic acid, adipic acid, salicylic acid, p-hydroxybenzoic acid, lactic acid, dihydroxybenzoic acid, citric acid, tartaric acid, and phthalic acid in any proportion.

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