A modified polymer preparation method, a composite additive for a lithium ion battery positive electrode, a preparation method and a lithium ion battery positive electrode slurry

Abstract

This application relates to a composite additive for lithium-ion battery cathodes, its preparation method, and a lithium-ion battery cathode slurry. The composite additive for lithium-ion battery cathodes comprises the following raw materials by mass percentage: 10%–30% phosphate ester; 2%–10% migration-resistant plasticizer; 10%–30% dispersant; and the remainder being solvent. The phosphate ester is obtained by esterification of a first raw material providing phosphate groups and a second raw material providing hydroxyl groups, with byproducts further complexed and separated after the esterification reaction. When applied to lithium-ion battery cathode slurries, this composite additive addresses the core contradictions of existing technologies, combining viscosity reduction and crack prevention effects. It further solves the problem of gas generation when using commercially available phosphate ester slurries, improving battery safety and consistency. This application also simplifies the process flow, improves production efficiency and economy, and enhances overall battery performance.

Description

Technical Field

[0001] This application relates to the fields of organic synthesis and lithium-ion battery materials, specifically to a method for preparing a modified polymer, a composite additive for lithium-ion battery cathodes, a preparation method thereof, and a lithium-ion battery cathode slurry. Background Technology

[0002] Driven by the lithium-ion battery industry's pursuit of higher energy density and lower manufacturing costs, increasing the solid content of cathode slurry has become a key process technology. High solid content slurry can reduce solvent usage, shorten drying time, and increase electrode coating density, meeting the demands of large-scale, high-efficiency production. However, the sharp increase in slurry viscosity due to high solid content leads to a series of processing challenges, such as poor leveling, difficult coating, and difficulty in removing air bubbles.

[0003] To address the challenges posed by high viscosity, the industry commonly introduces viscosity-reducing additives, such as various surfactants or small-molecule plasticizers. These additives adsorb onto the surface of cathode material particles, acting as lubricants and dispersants, thereby temporarily improving the flowability of the slurry. However, this improvement often comes at the cost of sacrificing the mechanical integrity of the electrode. During subsequent drying and rolling processes, these additives interfere with the film-forming properties and cohesion of the binder (such as PVDF), leading to insufficient electrode toughness, increased brittleness, and ultimately microcracks or even macroscopic cracking. Electrode cracking damages the conductive network, exacerbates side reactions, and directly impairs the cycle life and safety performance of the battery. While adding polymeric toughening agents (such as elastic microspheres) to prevent electrode cracking can improve electrode flexibility, these polymers significantly increase slurry viscosity, still requiring a large amount of solvent.

[0004] In high-solids-content cathode slurry systems, there is an inherent and irreconcilable contradiction between "processability" and "electrode integrity": viscosity reduction and crack prevention are mutually restrictive within the framework of traditional technologies, creating a tug-of-war where one gains at the expense of the other. Existing technologies have attempted to find compromises using common commercial phosphate esters (such as triphenyl phosphate), but their fixed molecular structures and singular functions prevent them from achieving synergy and balance in complex multi-component slurry systems, often resulting in shortcomings in viscosity reduction, compatibility, or long-term stability. Furthermore, the inventors discovered in their research and practice that commercially available common phosphate esters exhibit poor compatibility when mixed with highly alkaline systems such as high-nickel cathode materials, readily undergoing hydrolysis and side reactions with residual alkali on the surface, leading to gas generation and poor stability in the slurry. This instability not only affects the slurry's processing performance (e.g., generating bubbles and pinholes) but may also pose safety hazards during long-term battery cycling, limiting its application in high-performance lithium-ion batteries. Summary of the Invention

[0005] This application provides an additive that has both efficient viscosity reduction and crack prevention functions, and has good compatibility with the positive electrode system.

[0006] This application discloses a composite additive for the positive electrode of a lithium-ion battery, comprising a phosphate ester, wherein the phosphate ester is obtained by esterification of a first raw material for providing phosphate groups and a second raw material for providing hydroxyl groups, wherein byproducts are further complexed and separated after the esterification reaction.

[0007] Optionally, the raw materials for the composite additive include phosphate esters, plasticizers (migratory resistant), dispersants, and solvents.

[0008] This application discloses a composite additive for the positive electrode of lithium-ion batteries, wherein the raw materials have the following mass percentage composition:

[0009] Phosphate esters: 10%~30%; Migration-resistant plasticizers: 2%~10%; Dispersant 10%~30%; Solvent balance.

[0010] Several alternative methods are provided below, but they are not intended as additional limitations on the overall solution above. They are merely further additions or optimizations. Provided there are no technical or logical contradictions, each alternative method can be combined individually with respect to the overall solution above, or multiple alternative methods can be combined with each other.

[0011] Optionally, the raw materials may be composed of the following by weight percentage: Phosphate esters 15%~25%; Migration-resistant plasticizers: 3%~8%; Dispersant 15%~25%; Solvent balance.

[0012] Optionally, the raw materials may be composed of the following by weight percentage: Phosphate ester 20%; 5% migration-resistant plasticizer; Dispersant 20%; Solvent 55%.

[0013] Optionally, the phosphate ester is obtained by esterification of a first raw material for providing phosphate groups and a second raw material for providing hydroxyl groups, wherein the byproducts are further complexed and separated after the esterification reaction.

[0014] Optionally, the complexation separation is performed by treating the reaction system with an organic alcohol amine, wherein the amount of organic alcohol amine added is 1.2 to 2.0 times the theoretical total acid value molar amount of the reaction system.

[0015] Optionally, at least one of the first raw material and the second raw material has a hydrophobic long chain, and at least one has a polar functional group.

[0016] Optionally, the organic alcohol amine is selected from at least one of monoethanolamine, isopropanolamine, diethanolamine, and 2-amino-2-methyl-1-propanol.

[0017] Optionally, the organic alcohol amine is isopropanolamine and 2-amino-2-methyl-1-propanol, wherein isopropanolamine accounts for 60-80% of the total weight of the organic alcohol amine.

[0018] Optionally, the weight ratio of isopropanolamine to 2-amino-2-methyl-1-propanol is 7:3.

[0019] Optionally, the organic alcohol amine is isopropanolamine, diethanolamine, and 2-amino-2-methyl-1-propanol, wherein isopropanolamine accounts for 40-60% of the total weight of the organic alcohol amine, diethanolamine accounts for 25-40% of the total weight of the organic alcohol amine, and the balance is 2-amino-2-methyl-1-propanol.

[0020] Optionally, the weight ratio of isopropanolamine, diethanolamine, and 2-amino-2-methyl-1-propanol is 5:3:2.

[0021] Optionally, the molar ratio of the first raw material to the second raw material is 1:(2.0~3.5).

[0022] Optionally, the molar ratio of the first raw material to the second raw material is 1:2.5.

[0023] Optionally, the amount of organic alcohol amine added is 1.2 to 2.0 times the theoretical total acid value molar amount of the reaction system.

[0024] Optionally, the amount of organic alcohol amine added is 1.5 times the theoretical total acid value molar amount of the reaction system.

[0025] Optionally, the first raw material is selected from at least one of phosphorus pentoxide, phosphoric acid, phosphorus trichloride, trimethyl phosphate, tributyl phosphate, and isooctanol phosphate.

[0026] Optionally, the second raw material has a hydroxyl group for esterification with the first raw material. Preferably, the second raw material further contains an ether bond, i.e., it is a compound containing both a hydroxyl group and an ether bond.

[0027] Optionally, the second raw material is selected from at least one of block polyether, polyethylene glycol, octylphenol, plant phenol, octylphenol polyoxyethylene ether, isooctyl phosphate, and lauryl alcohol polyether.

[0028] The block polyether is a block copolymer of ethylene oxide (EO) and propylene oxide (PO) (EO-PO block polyether, after the reaction, one or both ends of the molecular chain are hydroxyl groups), with a number average molecular weight range of 1000~5000 g / mol and an HLB value range of 10~18, such as BASF Pluronic® series products (such as Pluronic® F127, CAS No. 9003-11-6).

[0029] The number-average molecular weight range of polyethylene glycol is 200~6000 g / mol. Specifically, polyethylene glycol 200 (CAS No. 25322-68-3, average molecular weight 190~210) and polyethylene glycol 6000 (CAS No. 25322-68-3, average molecular weight 5000~7000) can be used.

[0030] Octylphenol (CAS No. 140-66-9), industrial grade products such as the Triton™ X-100 series raw materials produced by DOW Chemical.

[0031] Plant phenols are a mixture of phenols extracted from natural plants, mainly including cashew phenol (CAS No. 37330-39-5) and guaiacol (CAS No. 90-05-1), with commercially available products such as the NX-2001 series produced by Cardolite.

[0032] Octylphenol polyoxyethylene ether (CAS No. 9036-19-5), EO addition number 4~40, such as DOW Chemical's Triton™ X-100 (EO=9-10).

[0033] Isooctyl phosphate (CAS No. 12645-31-7), industrial grade products such as Solvay's Rhodafac® PA series.

[0034] Laureth (CAS No. 9002-92-0), EO addition number 3~23, such as Croda's Brij® series.

[0035] Optionally, the molar ratio of the first raw material to the second raw material is 1:(2.0~3.5).

[0036] Optionally, the migration-resistant plasticizer is a terephthalate plasticizer.

[0037] Optionally, the migration-resistant plasticizer is selected from at least one of dioctyl terephthalate and di(tridecyl) terephthalate.

[0038] Optionally, the dispersant is a small molecule containing nitrogen.

[0039] Optionally, the dispersant is used to reduce the viscosity of the system.

[0040] Optionally, the dispersant contains nitrogen and has alkyl hydrophobic functional groups.

[0041] Optionally, the dispersant is selected from at least one of methyl hydrazine, hydroxyethyl hydrazine, anhydrous piperazine, isobutanolamine, polyetheramine, phenolic amide, alkylamide, N,N-diethylhydroxylamine, and N-methylethanolamine.

[0042] The polyetheramine is an amino-terminated polyether compound, CAS number 9046-10-0, with the general structural formula NH2-CH(CH3)-CH2-[O-CH2-CH(CH3)]. X -NH2 (difunctional) or trifunctional structure with glycerol as the initiator, with a number average molecular weight range of 230~4000 g / mol, preferably 230~2000 g / mol.

[0043] The phenolic amide is a compound formed by the condensation of cashew phenol or other plant phenols with polyamines, CAS number 129883-19-4, with a number-average molecular weight range of 500~3000 g / mol. Its molecular structure includes phenolic hydroxyl groups, long-chain alkyl groups, and amide groups, and it possesses both hydrophilic and lipophilic properties.

[0044] The alkylamides are selected from C8-C22 fatty acid amides or their derivatives, including: erucamide (CAS No. 112-84-5, molecular weight approximately 337), oleamide (CAS No. 301-02-0, molecular weight approximately 281), stearamide (CAS No. 124-26-5, molecular weight approximately 283) and alkylolamides.

[0045] This application also provides a method for preparing the aforementioned composite additive, comprising: In step S100, the starting materials are sequentially subjected to esterification reaction, neutralization treatment and post-treatment to prepare phosphate ester; Step S200: The phosphate ester is mixed with other raw materials to obtain the composite additive.

[0046] Optionally, step S100 specifically includes: Step S110: The first raw material and the second raw material are used to carry out an esterification reaction, wherein the molar ratio of the first raw material to the second raw material is 1:(2.0~3.5). Step S120: The reaction system after esterification is treated with an organic alcohol amine to obtain a neutralized reaction solution. The amount of organic alcohol amine added is 1.2 to 2.0 times the theoretical total acid value molar amount of the reaction system. Step S130: The neutralized reaction solution is subjected to solid-liquid separation at 50~80℃ to obtain a filtrate, and then the filtrate is dried to obtain the phosphate ester.

[0047] This application also provides a phosphate ester for preparing a composite additive for the positive electrode of a lithium-ion battery, wherein the content of monoesters in the phosphate ester is 60% to 75% based on the total mass of the phosphate ester as 100%.

[0048] Optionally, the monoester content in the phosphate ester is 65% to 72% (rounded to the nearest whole number). Optionally, the diester content in the phosphate ester is at least 20%.

[0049] Optionally, the diester content in the phosphate ester is 25% to 35%, for example, 26.5% to 32.5%.

[0050] This application also provides a phosphate ester for preparing a composite additive for the positive electrode of a lithium-ion battery, wherein the mass ratio of monoester to diester in the phosphate ester is 2.0~2.7:1.

[0051] This application also provides a phosphate ester for preparing a composite additive for the positive electrode of a lithium-ion battery, wherein the phosphate ester has a surface tension of 28.8~31.2 mN / m.

[0052] Optionally, the number average molecular weight of the phosphate ester is 700-2000, for example 800-1800, or 860-1580, or 1250-1420.

[0053] This application also provides a method for preparing the phosphate ester, which is obtained by esterification of a first raw material for providing phosphate groups and a second raw material for providing hydroxyl groups, wherein the byproducts are further complexed and separated after the esterification reaction. Specific details regarding the first raw material, the second raw material, and the complexation and separation process can be found in the foregoing.

[0054] This application also provides a method for preparing a modified polymer, namely, a method for preparing the phosphate ester, which is obtained by esterification reaction of a first raw material for providing phosphate groups and a second raw material for providing hydroxyl groups, wherein the by-products are further complexed and separated after the esterification reaction.

[0055] This application also provides a lithium-ion battery cathode slurry, comprising a base component and an additive, wherein the additive is the composite additive described in this application, and the amount of the additive added is 0.1 to 0.5% (by mass) of the base component, based on the amount of non-volatile component.

[0056] Optionally, the amount of the additive is 0.2-0.3%.

[0057] The amount of additives added is calculated as follows by weight percentage: additive / (positive electrode material + binder + conductive agent + additives) × 100%. Additives are calculated only by non-volatile components, such as only phosphate esters and migration-resistant plasticizers.

[0058] Optionally, the raw materials of the lithium-ion battery cathode slurry, by weight, include: Basic components: Cathode material 90~98; Adhesive 1~5; Conductive agent 0.5~2.5; Additives 0.1~0.5; Solvent 50~55.

[0059] Optionally, the raw materials of the lithium-ion battery cathode slurry, by weight, include: Basic components: Cathode material 97; Adhesive 1.8; Conductive agent 1; Additive 0.2; Solvent 54.

[0060] Similarly, when calculated by weight, additives are only considered as non-volatile components, such as phosphate esters and migration-resistant plasticizers.

[0061] This application also provides the application of the composite additive in the preparation of lithium-ion battery cathode slurry.

[0062] This application also provides a lithium-ion battery in which the positive electrode plate is prepared using the lithium-ion battery positive electrode paste described in this application.

[0063] Optionally, the electrode film resistance of the positive electrode plate is 31.8-43.3 ohm·cm².

[0064] Optionally, the electrode film resistance of the positive electrode plate is less than or equal to 40 ohm·cm².

[0065] Optionally, the electrode film resistance of the positive electrode plate is less than or equal to 35 ohm·cm².

[0066] Optionally, the areal density of the positive electrode plate is less than or equal to 17.8 mg / cm², and the electrode film resistance is less than or equal to 36.8 ohm·cm².

[0067] Optionally, the areal density of the positive electrode plate is less than or equal to 17 mg / cm², and the electrode film resistance is less than or equal to 36 ohm·cm².

[0068] The composite additives applied to lithium-ion battery cathode slurries in this application resolve the core contradictions of existing technologies, combining viscosity reduction and crack prevention effects. They further address the issue of gas generation when using commercially available phosphate ester slurries, thus improving battery safety and consistency. This application also simplifies the process flow, improves production efficiency and economy, and enhances the overall performance of the battery. Attached Figure Description

[0069] To more clearly illustrate the technical solutions in the embodiments of this application or the conventional technology, the drawings used in the description of the embodiments or the conventional technology will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0070] Figure 1 This is a schematic diagram of the surface of commercially available phosphate esters after direct mixing (preparation of lithium-ion battery cathode slurry) without treatment, showing that a large number of bubbles are generated; Figure 2 This is a schematic diagram of the surface of the slurry after the additives of the competing product have been mixed, showing that bubbles are continuously emerging; Figure 3 This is a schematic diagram of the surface of the composite additive slurry prepared according to the embodiments of this application, showing no gas generation; Figures 4-20 These are schematic diagrams of the surface morphology of lithium-ion battery positive electrode slurry coated onto electrode sheets prepared in Test Examples 1-17, respectively. Figures 21-26 These are schematic diagrams showing the surface morphology of lithium-ion battery cathode slurries after coating onto electrode sheets prepared in comparative test examples 1-6. Figure 27 This is a flowchart of a method for preparing a composite additive according to this application. Detailed Implementation

[0071] To make the above-mentioned objectives, features, and advantages of this application more apparent and understandable, the specific embodiments of this application are described in detail below with reference to the accompanying drawings. Many specific details are set forth in the following description to provide a thorough understanding of this application. However, this application can be implemented in many other ways different from those described herein, and those skilled in the art can make similar modifications without departing from the spirit of this application. Therefore, this application is not limited to the specific embodiments disclosed below.

[0072] This application addresses the multiple technical problems of existing commercially available phosphate esters, such as poor compatibility with cathode materials, easy gas generation, and inability to synergistically solve the high viscosity of high solid content cathode slurries and easy cracking of electrode sheets, due to their high acid impurities and high moisture content. It provides an anhydrous preparation method of high-purity, low-acid-value phosphate ester additives based on the phosphorus pentoxide route, the products obtained therefrom, and their application in lithium-ion battery cathodes.

[0073] One embodiment of this application provides a composite additive for the positive electrode of a lithium-ion battery, comprising a phosphate ester. The phosphate ester is obtained by esterification of a first raw material for providing phosphate groups and a second raw material for providing hydroxyl groups. After the esterification reaction, the byproducts are further complexed and separated. The raw materials of the composite additive may include the phosphate ester, a plasticizer (migratory resistant type), a dispersant, and a solvent.

[0074] See Figure 27 One embodiment of this application provides a method for preparing a composite additive, comprising: In step S100, the starting materials are sequentially subjected to esterification reaction, neutralization treatment and post-treatment to prepare phosphate ester; Step S200: The phosphate ester is mixed with other raw materials to obtain a composite additive.

[0075] Step S100 specifically includes: Step S110 is the esterification reaction: an esterification reaction is carried out using a first raw material and a second raw material, wherein the first raw material is used to provide a phosphate group and the second raw material is used to provide a hydroxyl group. For example, the first raw material is selected from at least one of phosphorus pentoxide, phosphoric acid, phosphorus trichloride, trimethyl phosphate, tributyl phosphate, and isooctanol phosphate.

[0076] The second raw material is an esterification raw material containing hydroxyl groups, such as a compound containing hydroxyl groups, specifically including C4~C6 compounds. 20 Straight-chain or branched fatty alcohols (such as butanol, octanol, dodecanol, hexadecyl alcohol, octadecanol, etc.), C6~C 20 The second raw material may be selected from at least one of the following: aryl alcohols or alkyl-substituted aryl alcohols (such as phenol, benzyl alcohol, octylphenol, nonylphenol, dodecylphenol, etc.), polyoxyethylene ether compounds (with the general formula RO-(CH2CH2O)-H), polyoxyethylene-polyoxypropylene block polyether compounds, and polyethylene glycol compounds.

[0077] When feeding materials, the second raw material is first put into the reaction flask. Under the protection of an inert gas (such as nitrogen or argon) and with efficient stirring, the first raw material is slowly and in batches added to the reaction flask. The molar ratio of the first raw material to the second raw material is 1:(2.0~3.5).

[0078] Some existing products have a high diester content, which, although effective in preventing cracking, results in high viscosity that affects dispersion. Other products have a high monoester content, which, while having good dispersibility, are less effective in preventing cracking. This application addresses the core contradiction of the prior art by improving the ratio of the first raw material to the second raw material, thus balancing dispersibility and crack prevention. As a further preferred option, the molar ratio of the first raw material to the second raw material is 1:(2.2~3), and even more preferred is 1:2.5.

[0079] Esterification is an exothermic reaction, and the reaction temperature is maintained at 60-100℃ using a temperature control device. After the feed is complete, the reaction is continued at this temperature range for 4-8 hours to ensure complete reaction.

[0080] Step S120, or neutralization treatment (anhydrous neutralization of the organic base): After the esterification reaction is completed, the reaction system is cooled to 40-60°C. An organic alcohol amine neutralizing agent is slowly added. The organic alcohol amine neutralizing agent is a C2-C6 alcohol amine organic base, selected from at least one of monoethanolamine, isopropanolamine, diethanolamine, and 2-amino-2-methyl-1-propanol. The amount added is 1.2-2.0 times the theoretical total acid value molar amount of the reaction system.

[0081] This application employs an esterification combined with anhydrous neutralization and purification process using organic bases to synthesize phosphate esters, achieving ultra-low acid value and ultra-low moisture content, thus improving compatibility with battery systems. The acid value and moisture content of the phosphate esters in this application are shown in the table below:

[0082] The organic alcohol amines (such as isopropanolamine) used in the neutralization process undergo a homogeneous neutralization reaction with the residual acidic byproducts in the reaction system, generating organic salts that are insoluble in the organic phase, which can be completely removed by filtration.

[0083] The theoretical total acid value of the reaction system refers to the amount of neutralizable acidic substances theoretically present in the system after the reaction, calculated based on the feed ratio of the esterification reaction, expressed in terms of H. + The calculation method is as follows: Based on the number of moles of the first raw material input, calculate the theoretical number of moles of alcohol required to completely convert it into neutral phosphate esters. Subtract the actual number of moles of alcohol input; the difference is the theoretical total acid value. When the amount of alcohol input is lower than the theoretical value, this difference is positive, representing the amount of acidic substances that must be present. When the amount of alcohol input is equal to or higher than the theoretical value, taking P2O5 as an example, the amount can be calculated as 4-6 moles of H per mole of P2O5. + A conservative estimate is made. The amount of organic alcohol amine neutralizer added should be 1.2-2.0 times the theoretical total acid value.

[0084] During neutralization, the reaction is stirred at 60-80℃ for 2-4 hours to allow the organic alcohol amine to fully react with all acidic byproducts such as polyphosphoric acid and phosphorous acid in the system, generating solids or high-boiling-point complexes.

[0085] Step S130, or post-treatment: The neutralized reaction solution is subjected to hot filtration or centrifugation, with the temperature maintained at 50-80°C (e.g., 50-70°C) throughout the process to thoroughly remove the solid residue generated by the reaction of organic alcohol amines with acidic byproducts. The filtrate is then vacuum dried to obtain the final product, which is the phosphate ester obtained by the improved process in this application. The entire process achieves anhydrous purification.

[0086] Unlike traditional water washing processes, the anhydrous environment in this application completely avoids contact between phosphate esters and water, preventing acid value rebound caused by hydrolysis. The entire neutralization and purification process does not introduce an aqueous phase, eliminating the introduction of moisture at the source. The primary amine structure of isopropanolamine ensures efficient and thorough neutralization, and its steric hindrance makes the generated organic salt easy to filter and separate. The tertiary amine structure of N,N-diethylhydroxylamine, while playing a neutralizing role, can also capture free radicals in the system, inhibit oxidation side reactions, and further improve the chemical stability of the product.

[0087] As a preferred embodiment, this application also provides a further improved scheme, namely, the organic alcohol amine adopts a compound system, for example, a binary system, namely, the organic alcohol amine is isopropanolamine and 2-amino-2-methyl-1-propanol, wherein isopropanolamine accounts for 60-80% of the total weight of the organic alcohol amine. As a preferred embodiment, the weight ratio of isopropanolamine to 2-amino-2-methyl-1-propanol is 7:3.

[0088] Alternatively, a ternary system can be used, in which the organic alcohol amine is isopropanolamine, diethanolamine, and 2-amino-2-methyl-1-propanol, wherein isopropanolamine accounts for 40-60% of the total weight of the organic alcohol amine, diethanolamine accounts for 25-40% of the total weight of the organic alcohol amine, and the balance is 2-amino-2-methyl-1-propanol. Preferably, the weight ratio of isopropanolamine, diethanolamine, and 2-amino-2-methyl-1-propanol is 5:3:2.

[0089] The compound system achieves comprehensive optimization of acid value, moisture content, viscosity stability, and membrane resistance through functional complementarity, and its synergistic effect far exceeds the sum of the individual components.

[0090] Of course, one embodiment of this application also provides a composite additive. The phosphate ester can be obtained by the preparation method described above, and the raw materials of the composite additive can be composed of the following mass percentages (the sum of all raw materials is 100%): Phosphate esters: 10%~30%; Migration-resistant plasticizers: 2%~10%; Dispersant 10%~30%; Solvent balance.

[0091] As a preferred option, the raw materials have the following mass percentage composition: Phosphate esters 15%~25%; Migration-resistant plasticizers: 3%~8%; Dispersant 15%~25%; Solvent balance.

[0092] As a further preferred option, the raw material composition by mass percentage is as follows: Phosphate ester 20%; 5% migration-resistant plasticizer; Dispersant 20%; Solvent 55%.

[0093] In this application, phosphate esters are the core functional component of the composite additive. Prepared using the improved method described in this application, they exhibit ultra-low acid value and moisture content, ensuring the chemical stability of the entire formulation. In the system, they primarily function as both viscosity reducers and internal plasticizers to prevent cracking.

[0094] This application uses migration-resistant plasticizers, such as terephthalate plasticizers, specifically at least one of dioctyl terephthalate and di(tridecyl) terephthalate. Traditional small-molecule plasticizers have a fundamental drawback in battery systems: easy volatility and migration. Their plasticizing effect rapidly declines with electrode drying and long-term cycling, leading to electrode embrittlement and cracking. Simultaneously, the migrated substances contaminate the electrolyte, damage interfacial stability, and catalyze gas-generating side reactions. While the large-molecule plasticizers used in this application typically increase film resistance, the phosphate esters in this application can improve or reduce film resistance, forming a functional complementarity with the large-molecule plasticizers. Furthermore, by combining the appropriate ratio of the two, the negative effects can be offset, achieving a balance between performance and material properties. Specifically, this application selects terephthalate plasticizers with excellent migration resistance and heat resistance, enabling them to be permanently anchored in the binder network. This ensures the long-term flexibility of the electrode while effectively preventing embrittlement and interfacial deterioration caused by plasticizer loss.

[0095] The dispersant in this application is selected from at least one of the following: small amine molecules, polymers containing strongly polar adsorption groups, and silane / titanium ester coupling agents. It achieves chemical anchoring and interface modification of the surface of positive electrode active material particles through functional groups such as amine groups, amide groups, and siloxane groups in the molecule. At the same time, it effectively prevents particle agglomeration, significantly reduces slurry viscosity, and improves dispersion uniformity by means of steric hindrance or electrostatic repulsion. Among them, small amine molecules (such as at least one of methyl hydrazine, hydroxyethyl hydrazine, anhydrous piperazine, isobutanolamine, polyetheramine, phenolic amide, alkylamide, N-methylethanolamine, and N,N-diethylhydroxylamine) have good compatibility and free radical scavenging ability, which can further improve the chemical stability of the system.

[0096] The solvent in this application, such as NMP, can serve as a carrier for the entire composite additive, ensuring that the functional components are uniformly mixed and easily dispersed in the positive electrode slurry.

[0097] Preparation Examples 1-5 Phosphate esters were prepared using different raw materials (see Table 1 for details of the raw materials used in Preparation Examples 1-5) in conjunction with the preparation methods described above. The specific steps included: The raw materials are stirred under the protection of an inert gas (such as nitrogen or argon). The first raw material is added, and the molar ratio of the first raw material to the second raw material is 1:2.5. The reaction temperature is maintained at 70°C. After the addition is complete, the reaction is continued to be carried out within this temperature range for 6 hours to ensure complete reaction.

[0098] After the esterification reaction was completed, the reaction system was cooled to 40°C, and the organic alcohol amine was slowly added. (Refer to the neutralizing reagents listed in Table 2 for the specific organic alcohol amines used in Examples 1-17 below.) The amount of organic alcohol amine added was 1.5 times the theoretical total acid value molar amount of the reaction system. The reaction was stirred at 60°C for 4 hours.

[0099] The neutralized reaction solution was subjected to hot filtration or centrifugation at 60°C to completely remove the solid residue generated by the reaction of the organic alcohol amine with the acidic byproducts. The filtrate was then vacuum dried to obtain the final product, phosphate ester.

[0100] Table 1

[0101] Table 1 shows the raw materials used in preparation examples 1-5.

[0102] In Table 1, abbreviations are explained as follows: OP refers to the octylphenol group, and -10 indicates that the polyoxyethylene chain contains an average of 10 oxyethylene units. Lauryl alcohol polyether-9 is a polyoxyethylene ether polymerized from lauryl alcohol (dodecyl alcohol) and 9 ethylene oxide units, with the general formula C0. 12 H 25 O(CH2CH2O)9H, where S represents homemade.

[0103]

[0104] In the table above regarding the testing items, isopropanolamine was selected as the neutralizing reagent used in the preparation of phosphate esters.

[0105] The phosphate ester products prepared in Examples 1-5 of this application show significant differences in key physicochemical properties compared with commercially available ordinary phosphate esters (represented by OP-10P): (1) Mono / Diester ratio: The content of phosphate monoesters in this application is as high as 65%~72%, and the mono / diester ratio is 2.0~2.7, which is significantly higher than the 48% and 0.97 of commercially available products. This structure gives the particles a stronger anchoring ability on the surface.

[0106] (2) Free phosphoric acid content: The free phosphoric acid content of the phosphate esters in this application is less than 0.35%, which is far superior to the 1.85% of commercially available products. Free phosphoric acid is the main cause of side reactions with the cathode material and gas generation in the slurry. This application reduces it to trace levels.

[0107] (3) Acid value and moisture: The phosphate ester of this application has an acid value of <0.1 mgKOH / g and a moisture content of <50 ppm, which is only a fraction of that of commercially available products, thus fundamentally ensuring the chemical stability of the slurry.

[0108] (4) Interfacial activity: The surface tension of the phosphate ester in this application is 28.8~31.2 mN / m, and the CMC is as low as (2.8~4.5)×10 - 4 The concentrations of these mol / L were significantly better than those of commercially available products (38.6 mN / m, 18.5 × 10⁻⁶ mol / L). -4 (mol / L), indicating that it has stronger interfacial adsorption capacity and higher molecular efficiency.

[0109] The synergistic optimization of the above-mentioned physicochemical indicators constitutes the core feature that distinguishes the phosphate ester of this application from existing products, and is also the physical property basis for its ability to simultaneously achieve multiple technical effects such as viscosity reduction, crack prevention, and non-gas generation.

[0110] Based on the above preparation examples, it can be understood that this application also provides one or more phosphate esters, wherein the monoester content in the phosphate ester is 60% to 75% based on the total mass of the phosphate ester as 100%, for example, the monoester content in the phosphate ester is 65% to 72%.

[0111] This application also provides a phosphate ester, wherein the mass ratio of monoester to diester in the phosphate ester is 2.0 to 2.7:1.

[0112] This application also provides a phosphate ester with a surface tension of 28.8~31.2 mN / m.

[0113] Examples 1-17 (including Comparative Examples 1-3) Examples 1-17 of this application provide a variety of composite additives for the positive electrode of lithium-ion batteries (lithium iron phosphate batteries with lithium iron phosphate as the positive electrode material), and the mass percentage composition of the raw materials is as follows: 20% phosphate ester 5% of migration-resistant plasticizers Dispersant 20% Solvent 55%.

[0114] The phosphate esters in Examples 1-17 were obtained from Preparation Examples 1-5. Comparative Examples 1-3 are also provided below, wherein: Comparative Example 1 is the blank group; Comparative Examples 2 and 3 are competing commercially available additives, among which: Comparative Example 2 (i.e., Competitor 1 is a polyether phosphate): Tridecyl alcohol polyether-10 phosphate (CAS: 9046-01-9, average molecular weight approximately 500 g / mol, active content ≥95%) was selected and diluted with NMP to prepare a solution with a solid content of 10%, which is the additive of Competitor 1. When preparing the positive electrode slurry, it is added at 0.5% of the mass of the active material (i.e., tridecyl alcohol polyether-10 phosphate accounts for 0.5% of the total weight of the basic components of the positive electrode slurry).

[0115] Comparative Example 3 (i.e., competitor 2 is polyurethane): Polyester-type thermoplastic polyurethane (such as polyethylene adipate-MDI type, with a number average molecular weight of about 30,000 g / mol) was selected, dissolved in NMP to prepare a solution with a solid content of 8%, which is the additive of competitor 2. When preparing the positive electrode slurry, it was added at 0.2% of the mass of the active material (i.e., polyester-type thermoplastic polyurethane accounts for 0.2% of the total weight of the basic components of the positive electrode slurry).

[0116] Comparative Examples 4-6 are composite additives formulated using commercially available phosphate esters.

[0117] The raw material composition of all embodiments and comparative examples is shown in the table below.

[0118] Table 2

[0119] Acid value and moisture content of the phosphate esters corresponding to each example

[0120] Table 2 describes the components and dosages of the composite additives in each embodiment and comparative example. In Table 2: S-OP-10P: See Preparation Example 1 for the esterification product; S-RP-98: See Preparation Example 2 for the esterified product; S-AEO-9P: See Preparation Example 3 for the esterification product; NMP: N-methylpyrrolidone; RP-98: Isooctyl phosphate; OP-10P: Commercially available phosphate ester; AEO-9P: Commercially available phosphate ester; DOTP: Dioctyl terephthalate; DTDP: Di(tridecyl) terephthalate; AMP-95: 2-Amino-2-methyl-1-propanol.

[0121] As shown in Table 2, in Example 10, monoethanolamine was used, resulting in an acid value of 0.28 mg KOH / g and a moisture content of 135 ppm. This is because monoethanolamine molecules are small, highly basic, and lack steric hindrance, leading to a vigorous neutralization reaction. The resulting organic salts are easily hygroscopic, causing a decrease in product purity. In Example 11, triethanolamine was used, resulting in an acid value of 0.35 mg KOH / g and a moisture content of 160 ppm. This is because triethanolamine is a tertiary amine, with weak basicity and insufficient neutralization ability. Furthermore, the strong hygroscopicity of its three hydroxyl groups leads to a high moisture content, and the resulting organic salts may partially dissolve in the organic phase, making complete removal difficult.

[0122] The remaining embodiments showed better results, especially Examples 12 and 13, which demonstrated a synergistic effect due to the use of a compound amine system. The ternary system is analyzed as an example below: (1) Functional complementarity: The primary amine structure of isopropanolamine provides the strongest neutralization ability of acidic byproducts, ensuring the realization of ultra-low acid value; the secondary amine structure of diethanolamine, while assisting in neutralization, can enhance the hydrogen bonding with the particle surface with its two hydroxyl groups, thus assisting in dispersion; the sterically hindered primary amine of AMP-95 plays a pH buffering role in the later stage of the reaction, preventing instability caused by local over-alkali or over-acidity.

[0123] (2) Structural matching: The three alkanolamines have different molecular sizes, steric hindrances and hydrophilic-hydrophobic balances, forming a multi-layered interfacial adsorption layer in the reaction system, which not only ensures the thoroughness of the neutralization reaction, but also endows the phosphate ester molecules with better interfacial activity.

[0124] (3) Enhanced stability: The compound system has a stronger tolerance to pH fluctuations during the reaction process, which reduces the sensitivity of product quality to process parameters and makes it easier to achieve stable industrial production.

[0125] Lithium-ion battery cathode slurries were prepared using the additives (hereinafter referred to as additives) from Examples 1-17 and Comparative Examples 1-6 described above, and were tested accordingly. The preparation process of the lithium-ion battery cathode slurry is as follows: The cathode material LFP, binder PVDF, conductive agent SP, and NMP were mixed in a weight ratio of 97:1.8:1:54. After stirring at 500 rpm for 30 minutes, the additives of each example and the comparative example (where the additives in comparative example 2 were 0.5%) with a solid content of 0.2% were weighed and added to the slurry. Finally, the cathode slurry was obtained by vacuum degassing.

[0126] Taking an additive dosage of 0.2% as an example, it can be converted to 0.2 parts by weight, that is, positive electrode material LFP: binder PVDF: conductive agent SP: additive = 97:1.8:1:0.2. Of course, when calculating the additive dosage, only the non-volatile components in the additive are calculated, or it can be understood as the components remaining after coating the electrode and drying. For each embodiment of this application, the additive dosage is calculated only by weight of phosphate ester and migration-resistant plasticizer.

[0127] See Figures 1-3 As can be seen in the image: Figure 1 This indicates that after the composite additives in Comparative Example 4 were used to prepare the positive electrode slurry, a large number of bubbles were generated in the positive electrode slurry. Figure 2 This indicates that after the positive electrode slurry was prepared using the competitor's additives in Comparative Example 2, bubbles continuously emerged from the surface of the positive electrode slurry. Figure 3 This indicates that after the composite additive prepared in Example 1 of this application is used to prepare the positive electrode slurry, no gas is generated on the surface.

[0128] Test Results The positive electrode slurries of Test Examples 1 to 17 were respectively made using the composite additives of Examples 1 to 17, and the positive electrode slurries of Comparative Test Examples 1 to 6 were respectively made using the composite additives of Comparative Examples 1 to 6. The viscosity and standing viscosity were tested respectively.

[0129] Table 3

[0130] Table 3 shows the viscosity and settling viscosity test results of the positive electrode slurry for test examples 1-17 and comparative test examples 1-6.

[0131] As can be seen from the table, the positive electrode slurry using the composite additives of this application has lower viscosity and lower settling viscosity.

[0132] Membrane resistance and areal density After the positive electrode pastes of Test Examples 1-17 and Comparative Test Examples 1-6 were coated onto the electrode sheets, the film resistance and areal density were tested.

[0133] For example, the positive electrode slurry prepared according to the proportions in each embodiment is degassed under vacuum and then coated onto a 16 μm thick aluminum foil using an automatic blade coater. The blade gap is adjusted to 250 μm, and the coating speed is 10 mm / s. The coated electrode is then dried in a 100°C forced-air drying oven for 20 minutes, and then transferred to a 120°C vacuum drying oven for 12 hours to obtain the positive electrode to be tested.

[0134] Areal density test: The positive electrode sheet to be tested can be punched into a circular sheet with a diameter of 14 mm using a punching machine, and the areal density (mg / cm²) can be weighed and calculated using an electronic balance.

[0135] Membrane resistance testing: A four-probe resistivity meter can be used to test the membrane resistance of the positive electrode. Before testing, cut the electrode into samples with a size of not less than 4 cm × 4 cm, ensuring that the samples are flat and wrinkle-free. Place the four-probe probe vertically and gently on the coating surface of the electrode, set the test current to 10 mA (adjustable according to the sample resistivity range), and measure at least 3 different locations for each sample. Take the average value as the membrane resistance value of the electrode.

[0136]

[0137] Table 4 shows the test results of film resistance and areal density of the positive electrode slurry of Test Examples 1-17 and Comparative Test Examples 1-6 after coating the electrode sheet.

[0138] As shown in Table 4, after coating the positive electrode slurry using the composite additives of this application, under similar areal density conditions (the overlap area between the test examples and the comparative test examples is 15.5-19.7 mg / cm²), the electrode film resistance of test examples 1-9 (31.8-43.3 ohm·cm²) using the additives of this application is significantly lower than that of comparative test examples 1-6 (44.7-63.6 ohm·cm²), with an average reduction of over 30%. This indicates that the composite additives of this application can effectively optimize the electrode microstructure, improve the interfacial contact between the active material, conductive agent, and binder, and construct a more continuous, low-resistance conductive network, thereby laying the foundation for improving the rate performance and cycle life of the battery. Even at higher areal densities (>19 mg / cm²), the membrane resistance of test examples 6-9 remained stable at around 40 ohm·cm², while the membrane resistance of the comparative examples increased to 53-64 ohm·cm² under similar loads. This comparison further demonstrates that the additives of this application can stably play their role in optimizing the electrode structure over a wide range of areal densities, and their advantages become more prominent as the areal density increases.

[0139] Combination Figures 4-20 Schematic diagram of the surface morphology of the lithium-ion battery positive electrode slurry prepared in Test Examples 1-17 after coating the electrode sheet; Figures 21-26 These are schematic diagrams showing the surface morphology of lithium-ion battery cathode slurry coated onto electrode sheets prepared in comparative test examples 1 to 6.

[0140] As shown in the figure, the electrode sheet coated with the lithium-ion battery positive electrode slurry of this application has a smooth surface without cracks, exhibiting excellent compatibility. In contrast, the comparative test examples showed varying degrees of cracking and blistering, indicating poor compatibility.

[0141] The plasticizer and phosphate ester in this application work synergistically. The plasticizer primarily acts on the PVDF binder bulk, lowering its glass transition temperature; the phosphate ester simultaneously acts on the interface between the PVDF chains and the active material, serving as an anchor and bridge. This combination imparts excellent flexibility to the electrode to prevent cracking while maintaining necessary mechanical strength and preventing plasticizer migration, ensuring interfacial stability during long-term battery cycling. Furthermore, the polar groups of the phosphate ester in this composite additive system can interact with the hydroxyl groups on the surface of the cathode material, further strengthening the interfacial bonding.

[0142] The dispersant and phosphate ester in this application can synergistically act on the surface of the positive electrode active material and conductive agent particles. The dispersant provides the main dispersion stabilizing force through strong adsorption and steric hindrance; the phosphate ester further reduces the frictional resistance between particles through adsorption and molecular lubrication. The combination of the two forms a dual stabilization mechanism, which not only significantly reduces the viscosity of the slurry, but also ensures the dispersion stability and uniformity of the slurry during long-term standing, thereby obtaining a positive electrode sheet with uniform coating and consistent performance.

[0143] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the patent application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the scope of protection of this application. Therefore, the patent protection scope of this application should be determined by the appended claims.

Claims

1. A composite additive for the positive electrode of a lithium-ion battery, characterized in that, The raw materials are composed of the following percentages by mass: Phosphate esters: 10%~30%; Migration-resistant plasticizers: 2%~10%; Dispersant 10%~30%; Solvent balance; The phosphate ester is obtained by esterification of a first raw material for providing phosphate groups and a second raw material for providing hydroxyl groups, wherein the byproducts are further complexed and separated after the esterification reaction.

2. The composite additive for the positive electrode of a lithium-ion battery according to claim 1, characterized in that, The raw materials are composed of the following percentages by mass: Phosphate esters 15%~25%; Migration-resistant plasticizers: 3%~8%; Dispersant 15%~25%; Solvent balance.

3. The composite additive for the positive electrode of a lithium-ion battery according to claim 2, characterized in that, The raw materials are composed of the following percentages by mass: Phosphate ester 20%; 5% migration-resistant plasticizer; Dispersant 20%; Solvent 55%.

4. The composite additive for the positive electrode of a lithium-ion battery according to claim 1, characterized in that, The complexation separation is achieved by treating the reaction system with an organic alcohol amine, wherein the amount of organic alcohol amine added is 1.2 to 2.0 times the theoretical total acid value molar amount of the reaction system.

5. The composite additive for the positive electrode of a lithium-ion battery according to claim 4, characterized in that, The first raw material is selected from at least one of phosphorus pentoxide, phosphoric acid, phosphorus trichloride, trimethyl phosphate, tributyl phosphate, and isooctanol phosphate; The second raw material is selected from at least one of block polyether, polyethylene glycol, octylphenol, phytophenol, octylphenol polyoxyethylene ether, isooctyl phosphate, and lauryl alcohol polyether; The organic alcohol amine is selected from at least one of monoethanolamine, isopropanolamine, and diethanolamine.

6. The composite additive for the positive electrode of a lithium-ion battery according to claim 5, characterized in that, The molar ratio of the first raw material to the second raw material is 1:(2.0~3.5).

7. The composite additive for the positive electrode of a lithium-ion battery according to claim 4, characterized in that, The migration-resistant plasticizer is selected from at least one of dioctyl terephthalate and di(tridecyl) terephthalate; The dispersant is selected from at least one of methyl hydrazine, hydroxyethyl hydrazine, anhydrous piperazine, isobutanolamine, polyetheramine, phenolic amide, alkylamide, N,N-diethylhydroxylamine, and N-methylethanolamine.

8. The method for preparing the composite additive according to any one of claims 1 to 7, characterized in that, include: Step S100 involves sequentially performing esterification, neutralization, and post-treatment to prepare a phosphate ester, specifically including: Step S110: The first raw material and the second raw material are used to carry out an esterification reaction, wherein the molar ratio of the first raw material to the second raw material is 1:(2.0~3.5). Step S120: The reaction system after esterification is treated with an organic alcohol amine to obtain a neutralized reaction solution. The amount of organic alcohol amine added is 1.2 to 2.0 times the theoretical total acid value molar amount of the reaction system. Step S130: The neutralized reaction solution is subjected to solid-liquid separation at 50~80℃ to obtain filtrate, and then the filtrate is dried to obtain the phosphate ester; Step S200: The phosphate ester is mixed with other raw materials to obtain the composite additive.

9. A lithium-ion battery positive electrode slurry, comprising basic components and a solvent, characterized in that, The basic component contains an auxiliary agent, which is a composite auxiliary agent as described in any one of claims 1 to 7. The amount of the auxiliary agent added, based on the non-volatile component, is 0.1% to 0.5%. The raw materials, by weight, include: Basic components: Cathode material 90~98; Adhesive 1~5; Conductive agent 0.5~2.5; Additives 0.1~0.5; Solvent 50~55.

10. A method for preparing a modified polymer, characterized in that, The product is obtained by esterification of a first raw material for providing phosphate groups and a second raw material for providing hydroxyl groups, wherein the byproducts are further complexed and separated after the esterification reaction. The first raw material is selected from at least one of phosphorus pentoxide, phosphoric acid, phosphorus trichloride, trimethyl phosphate, tributyl phosphate, and isooctanol phosphate; The second raw material is selected from at least one of block polyether, polyethylene glycol, octylphenol, plant phenol, octylphenol polyoxyethylene ether, isooctyl phosphate, and lauryl alcohol polyether.

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