Slurry dispersion method based on compounding of carboxymethyl cellulose and dopamine and application

Abstract

The invention relates to the technical field of lithium ion batteries, and discloses a slurry dispersion method based on compounding of carboxymethyl cellulose and dopamine and application. The method comprises the following steps: dissolving carboxymethyl cellulose in water; adding dopamine hydrochloride into the solution under the conditions of nitrogen protection and alkalescence; then, through multi-stage programmed temperature and pressure regulation and control, low-temperature pre-adsorption and temperature and pressure rise synergistic reaction are carried out, and the composite dispersing agent is prepared. In the composite dispersing agent, a structure formed by self-polymerization of dopamine is anchored on a carboxymethyl cellulose chain segment, so that a strong adsorption effect can be generated on a negative electrode active material and conductive agent particles at the same time, and effective steric hindrance is formed. When the composite dispersing agent is used for preparing negative electrode slurry, the storage stability of the slurry can be remarkably improved, and a negative electrode active material and a conductive agent form a uniform three-dimensional conductive network in an electrode, so that the cycle performance and the capacity retention rate of a lithium ion battery are effectively improved.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, specifically to a slurry dispersion method and application based on a composite of carboxymethyl cellulose and dopamine. Background Technology

[0002] Lithium-ion batteries, due to their high energy density and long cycle life, have become the primary energy storage device for modern electronic devices and electric vehicles. The performance of lithium-ion batteries largely depends on the manufacturing process of their electrodes, with the preparation of the negative electrode slurry being one of the key steps determining the final electrode structure and electrochemical performance. The negative electrode slurry is typically a complex multiphase suspension system composed of negative electrode active materials (such as graphite), conductive agents (such as acetylene black), binders, and solvents.

[0003] In the slurry preparation process, it is necessary to break up the agglomerated solid particles, especially conductive agent particles with small size and high specific surface area, and uniformly disperse them among the active material particles to construct a continuous and complete three-dimensional conductive network. However, due to the differences in particle size, surface chemical properties, and zeta potential between the negative electrode active material and the conductive agent in the dispersion medium, the conductive agent particles have a significant tendency to re-agglomerate due to van der Waals forces. This agglomeration directly leads to solid-phase sedimentation during the slurry settling process, reducing the system stability.

[0004] Currently, carboxymethyl cellulose (CMC) is commonly used in industrial production as both a binder and a dispersant. CMC molecules adsorb onto particle surfaces due to their long-chain structure, maintaining particle dispersion through electrostatic repulsion and steric hindrance. However, the physical adsorption force between CMC molecules and conductive agent particle surfaces is relatively weak, making it difficult to form a robust adsorption layer. Therefore, under prolonged storage or shear stress changes, dispersed conductive agent particles are prone to desorption and re-aggregation. This not only affects the rheological properties and coating uniformity of the slurry, but more importantly, the slurry's inhomogeneity directly extends to the final electrode coating. Aggregation of the conductive agent within the electrode causes discontinuities in the conductive network, increasing the electrode's charge transfer resistance. During battery cycling, this heterogeneous structure leads to uneven current density distribution, resulting in intensified local polarization, excessive growth of the solid electrolyte interphase (SEI) film, and irreversible loss of active lithium, ultimately manifesting as a rapid decline in battery capacity retention with increasing cycle count. Summary of the Invention

[0005] The purpose of this invention is to provide a slurry dispersion method and application based on a composite of carboxymethyl cellulose and dopamine, aiming to solve the technical problems of uneven dispersion and poor stability of negative electrode slurries in the prior art, which in turn affect electrode performance.

[0006] To achieve the above objectives, the present invention provides the following technical solution: The first aspect of this invention provides a slurry dispersion method based on a composite of carboxymethyl cellulose and dopamine. This method utilizes the self-polymerization properties of dopamine and its reaction with functional groups on carboxymethyl cellulose segments under weakly alkaline conditions to construct a composite dispersant with a unique network structure. The structural feature of this composite dispersant is that the rigid adsorption cores formed by dopamine are firmly anchored to the surface of the negative electrode material, while the flexible long chains provided by carboxymethyl cellulose extend into the solvent, forming an effective steric hindrance layer. This combination of rigidity and flexibility enables both strong surface adsorption and efficient steric hindrance, thereby significantly improving the dispersion effect and long-term stability of the negative electrode active material and conductive agent in aqueous systems.

[0007] The method includes the following steps: S1. Preparing a composite dispersant, wherein the step of preparing the composite dispersant includes: S11. Provide a homogeneous aqueous solution of carboxymethyl cellulose; S12. Add dopamine hydrochloride to the homogeneous carboxymethyl cellulose aqueous solution and adjust the pH of the system to 8.0-8.5 using a neutralizing agent to obtain a pH-adjusted mixed system; S13. A multi-stage composite reaction is carried out on the pH-adjusted mixed system to obtain the reaction product; S14. The reaction product is post-processed to obtain a composite dispersant.

[0008] S2. Preparing a negative electrode slurry using the composite dispersant, wherein the step of preparing the negative electrode slurry includes: S21. Add the negative electrode active material and the conductive agent to deionized water for premixing to obtain a premixed solution; S22. The composite dispersant obtained in step S1 is added to the premixed liquid for final dispersion, thereby obtaining the negative electrode slurry.

[0009] In one specific implementation, in step S11, the preparation conditions of the homogeneous carboxymethyl cellulose aqueous solution are precisely controlled. Carboxymethyl cellulose powder with a degree of substitution of 0.7-1.2 and a viscosity of 1000-2500 mPa·s for a 1% aqueous solution is selected to ensure suitable solubility and chain length. In a double-walled glass reactor, the powder is slowly added at a rate of 0.1-0.5 g / min under constant temperature of 30-40°C and initial stirring at 300-500 r / min. This operation prevents macroscopic agglomeration of the powder. After the addition is complete, the mechanical stirring speed is increased to 500-800 r / min, supplemented by ultrasonic treatment at 200-500 W and 20-40 kHz for 30-60 minutes. The ultrasonic cavitation effect is used to disperse microscopic agglomerates, ultimately obtaining a homogeneous solution with a mass concentration of 0.5%-5%. To quantify the homogeneity of the solution, a dynamic light scattering instrument is used for detection, controlling the coefficient of variation of particle size distribution to be no greater than 5%.

[0010] In one specific implementation plan, in step S12, the system environment and feeding method are strictly controlled.

[0011] First, high-purity nitrogen gas with a purity of not less than 99.999% is introduced into the homogeneous carboxymethyl cellulose aqueous solution for 25-35 minutes (flow rate 0.5-1L / min) to remove dissolved oxygen in the system and inhibit the uncontrolled rapid oxidation of dopamine.

[0012] Subsequently, under nitrogen protection and stirring at 800-1000 rpm, dopamine hydrochloride is added in 2-5 portions (3-10 minutes apart) through a solid feeding funnel. This stepwise feeding method facilitates the uniform dispersion of dopamine in the system.

[0013] Finally, the pH of the system was precisely adjusted to 8.0-8.5 by adding a neutralizing agent (0.05-0.15 mol / L tris(hydroxymethyl)aminomethane base solution or 0.4-0.6 mol / L sodium hydroxide solution) dropwise at a rate of 0.5-2 mL / min using an automatic potentiometric titrator. This pH range is necessary for activating dopamine self-polymerization and its reactivity with carboxymethyl cellulose. The temperature was monitored in real time during the addition process and controlled to not exceed 40°C to prevent localized overheating and side reactions.

[0014] In one specific implementation, the composite reaction in step S13 is a gradient-controlled procedure, specifically divided into two stages: a. Low-temperature pre-adsorption stage: The pH-adjusted mixture is transferred to a programmable temperature-controlled high-pressure reactor and reacted for 1.5-2.5 hours at 20-30℃ and a stirring rate of 500-800 r / min under a nitrogen micro-positive pressure of 0.01-0.02 MPa. The mild conditions in this stage primarily promote the adsorption of dopamine molecules onto carboxymethyl cellulose segments through non-covalent interactions such as hydrogen bonds and van der Waals forces, forming an ordered pre-assembled structure. The reaction progress is monitored using in-situ infrared spectroscopy. When the peak intensity ratio of the hydroxyl characteristic peak of carboxymethyl cellulose to the amino characteristic peak of dopamine stabilizes within the range of 0.3-0.5, it indicates that the pre-adsorption has reached equilibrium.

[0015] b. Synergistic Reaction Stage with Heating and Pressure Increase: For the pre-adsorbed product, the reaction is first carried out at 25-35℃ and 0.08-0.12MPa for 0.5-1.5 hours to further consolidate the non-covalent bond interaction. Subsequently, the temperature is increased to 40-50℃ at a rate of 0.3-0.7℃ / min, and the pressure is simultaneously increased to 0.18-0.22MPa, while the stirring rate is increased to 900-1100r / min. The heating and pressure increase provides the necessary activation energy for dopamine oxidation, self-polymerization, and covalent reactions such as Michael addition or Schiff base formation with carboxymethyl cellulose functional groups, thereby forming a stable covalent cross-linked network based on the pre-assembled structure. The endpoint of the reaction is determined by in-situ monitoring: when the rate of change of absorbance at 280nm in the in-situ UV-Vis spectrum is not higher than 5% / h, or the mass growth rate measured by the quartz crystal microbalance is stable at 0.5-1μg / cm³. 2 When the value is within the range of ·min, it indicates that the reaction has entered the steady-state period.

[0016] In one specific implementation, the post-processing procedure in step S14 aims to maintain the formed composite network structure. A gradient cooling and depressurization method is employed, with depressurization at a rate of 0.05 MPa / h–0.1 MPa / h and cooling at a rate of 2 °C / h–5 °C / h. This gradual change in conditions avoids structural collapse caused by rapid phase transitions or abrupt changes in the solvent environment. Finally, filtration is performed using a hydrophilic / hydrophobic bilayer composite filter membrane with a pore size of 0.2–0.3 μm to remove unreacted small molecules or byproducts from the system.

[0017] In one specific implementation, in step S21, the negative electrode active material (such as at least one of graphite, silicon-based material, and lithium titanate) and the conductive agent (such as at least one of superconducting carbon black, carbon nanotubes, and acetylene black) are added to deionized water at a mass ratio of (80-95):(5-20) and premixed for 10-30 minutes at a stirring rate of 500-1000 r / min.

[0018] In one specific implementation, in step S22, the prepared composite dispersant is added to the premixed solution at an amount of 0.5%-3% of the mass of the negative electrode active material. Subsequently, the stirring rate is increased to 800-1500 r / min, and final dispersion is carried out at a temperature of 20-40°C for 2-6 hours to ensure that the composite dispersant fully interacts with the material surface.

[0019] A second aspect of this invention provides the application of a negative electrode slurry prepared by any of the foregoing methods in a lithium-ion battery. The negative electrode slurry is coated onto a current collector and then processed through drying, rolling, and other steps to form a negative electrode sheet. Because the active material and conductive agent in the slurry are highly uniformly distributed, the resulting electrode coating also exhibits excellent uniformity. This uniformity effectively reduces the internal impedance of the electrode, promotes uniform migration and reaction of lithium ions within the electrode bulk phase, and reduces the risk of localized polarization and lithium dendrite growth caused by uneven current density distribution. Therefore, lithium-ion batteries prepared using this negative electrode slurry exhibit higher initial coulombic efficiency, better rate performance, and longer cycle life in terms of electrochemical performance.

[0020] This invention provides a slurry dispersion method and its application based on a carboxymethyl cellulose and dopamine composite. It has the following beneficial effects: 1. This invention prepares a structurally specific composite dispersant by setting a multi-stage procedure of low-temperature pre-adsorption and synergistic temperature and pressure increase reaction, combined with pH control and inert atmosphere protection. In the molecular structure of this dispersant, the region formed by dopamine polymerization can strongly adsorb onto the surface of the negative electrode material, while the region formed by carboxymethyl cellulose segments provides steric hindrance in the solvent. This specific structure enables the negative electrode active material and the conductive agent to achieve a long-term stable dispersion state in the slurry system, reducing the sedimentation rate of the slurry.

[0021] 2. In the preparation process of the composite dispersant, this invention introduces in-situ infrared spectroscopy, in-situ ultraviolet-visible spectroscopy, and a quartz crystal microbalance for real-time monitoring, and sets quantitative physical indicators (such as peak intensity ratio, absorbance change rate, and mass growth rate) for judging the reaction progress. This method enables objective determination of the composite reaction process and endpoint, reduces reliance on operational experience, ensures the consistency of structure and performance between batches of the prepared composite dispersant, and improves the repeatability of the process.

[0022] 3. The negative electrode slurry provided by this invention, due to the uniform distribution of the negative electrode active material and conductive agent, can form a homogeneous electrode coating and conductive network during subsequent electrode fabrication. This reduces the charge transfer resistance and concentration polarization of the electrode, thereby improving the electrochemical performance of lithium-ion batteries assembled using this electrode, specifically manifested in improved capacity retention during cycling and improved high-rate charge-discharge performance. Attached Figure Description

[0023] Figure 1 This is a schematic diagram illustrating the working principle of the composite dispersant of the present invention; Figure 2 This is a SEM image of the slurry from Example 3 of the present invention; Figure 3 The graphs show the capacity retention rates after 500 cycles for Examples 1 and 3 of the present invention. Detailed Implementation

[0024] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0025] Experimental materials and equipment: The main raw materials and reagents used in the following examples and comparative examples have the following sources and specifications. Reagents not specifically mentioned are all commercially available analytical grade or higher grade products.

[0026] Main raw materials and reagents: Sodium carboxymethyl cellulose, CAS No.: 9004-32-4; Dopamine hydrochloride, CAS No.: 62-31-7; Tris(hydroxymethyl)aminomethane, CAS No.: 77-86-1; Graphite, CAS No.: 7782-42-5; Acetylene black, CAS No.: 1333-86-4.

[0027] Examples 1-3: Example 1:

[0028] Preparation of composite dispersants: First, a homogeneous carboxymethyl cellulose (CMC) aqueous solution was prepared. 100 ml of deionized water with a conductivity not exceeding 10 μS / cm was placed in a double-walled glass reactor. Under constant temperature water bath conditions of 40°C, 1 g of carboxymethyl cellulose (CMC) powder was slowly added at a stirring rate of 0.5 g / min at a stirring rate of 500 r / min. The degree of substitution of the CMC was 0.7-1.2, and the viscosity of its 1% aqueous solution was 1000-2500 mPa·s. After the addition was complete, ultrasonic-assisted dispersion with a power of 200 W and a frequency of 20 kHz was activated, while mechanical stirring was maintained at 500 r / min for 30 minutes until the powder was completely dissolved. The particle size distribution of the obtained solution was measured using a dynamic light scattering instrument, confirming that its coefficient of variation was not greater than 5%, thus obtaining a 1% homogeneous CMC aqueous solution.

[0029] Next, the reaction system was pretreated and pH adjusted. High-purity nitrogen gas (99.999% purity) was bubbled into the homogeneous carboxymethyl cellulose aqueous solution obtained in step 1 at a flow rate of 0.6 L / min for 30 minutes to remove dissolved oxygen. Then, under nitrogen protection and stirring at 800 rpm, 0.1 g of dopamine hydrochloride was added in three portions through a solid feeding funnel, with each addition 5 minutes apart. Next, using an automatic potentiometric titrator, a 0.1 mol / L tris(hydroxymethyl)aminomethane (Tris) base solution was added dropwise to the system at a rate of 1 mL / min until the pH reached 8.0. The system temperature was monitored in real time during the addition to ensure it did not exceed 40°C.

[0030] In a preferred embodiment of the invention, the pH of the system is adjusted to 8.0. However, those skilled in the art will understand that the pH value can be selected within a weakly alkaline range to promote the self-polymerization of dopamine; for example, the pH value can be controlled within the range of 7.5 to 9.0. Furthermore, the alkaline reagent used is not limited to tris(hydroxymethyl)aminomethane; other inorganic or organic bases that do not adversely affect the main reaction, such as sodium bicarbonate solution or dilute sodium hydroxide solution, can also be used to adjust the pH.

[0031] Then, a multi-stage composite reaction was carried out. The pH-adjusted mixture from step 2 was transferred to a temperature-controlled high-pressure reactor, sealed, and nitrogen was introduced to purge the air inside the reactor, establishing a nitrogen micro-positive pressure of 0.01 MPa. The low-temperature pre-adsorption stage reaction was carried out at a constant temperature of 20°C and a stirring rate of 500 r / min for 2 hours. During the reaction, real-time monitoring was performed using an in-situ infrared spectroscopy instrument. When the characteristic peak of the hydroxyl group of carboxymethyl cellulose (located at 3400 cm⁻¹) was observed... -1 The characteristic amino peak of dopamine (located at 3300 cm⁻¹) -1When the peak intensity ratio of the adsorption peak stabilizes in the range of 0.3-0.5, the pre-adsorption stage ends.

[0032] Subsequently, the reaction proceeded to a synergistic heating and pressurization phase. First, the reaction was carried out at 30℃ and 0.1MPa for 1 hour. Then, the system temperature was increased to 45℃ at a heating rate of 0.5℃ / min, while the pressure was simultaneously increased to 0.2MPa and the stirring rate to 900 r / min. During the reaction, real-time monitoring was performed using in-situ UV-Vis spectroscopy and a quartz crystal microbalance. The reaction was considered successful when the absorbance change rate at 280nm was no higher than 5% / h, and the mass growth rate measured by the quartz crystal microbalance remained stable at 0.5-1 μg / cm³. 2 When the reaction is within the range of min, it is considered complete.

[0033] In a preferred embodiment of the invention, the final temperature of the synergistic temperature and pressure increase reaction is 45°C, and the final pressure is 0.2 MPa. However, to achieve a controlled complex reaction, the reaction temperature can be selected in the range of 35°C to 60°C, and the reaction pressure can be selected in the range of 0.1 MPa to 0.5 MPa. The total reaction time is typically 2 to 12 hours, depending on the selected temperature and pressure conditions.

[0034] Finally, post-processing was performed. After the reaction was completed, the reaction product was subjected to gradient cooling and depressurization treatment, with the depressurization rate controlled at 0.1 MPa / h and the cooling rate controlled at 5 °C / h. Finally, the cooled product was filtered using a hydrophilic / hydrophobic bilayer composite filter membrane with a pore size of 0.22 μm to obtain the composite dispersant.

[0035] Preparation of negative electrode slurry: 90g of graphite and 10g of acetylene black were added to 50mL of deionized water and premixed at a stirring rate of 600r / min for 20 minutes. Then, 2g of the prepared composite dispersant was added to the premix, the stirring rate was increased to 1000r / min, and dispersion was continued for 4 hours to finally obtain the negative electrode slurry.

[0036] Example 2:

[0037] Preparation of composite dispersants: First, a homogeneous carboxymethyl cellulose (CMC) aqueous solution was prepared. 100 ml of deionized water with a conductivity not exceeding 10 μS / cm was placed in a double-walled glass reactor. Under constant temperature water bath conditions of 40°C, 2 g of carboxymethyl cellulose (CMC) powder was slowly added at a stirring rate of 0.4 g / min at a stirring rate of 500 r / min. The degree of substitution of the CMC was 0.7-1.2, and the viscosity of its 1% aqueous solution was 1000-2500 mPa·s. After the addition was complete, ultrasonic-assisted dispersion at a power of 300 W and a frequency of 30 kHz was activated, while mechanical stirring was maintained at 500 r / min for 45 minutes until the powder was completely dissolved. The particle size distribution of the obtained solution was measured using a dynamic light scattering instrument, confirming that its coefficient of variation was not greater than 5%, thus obtaining a homogeneous CMC aqueous solution with a mass concentration of 2%.

[0038] Next, the reaction system was pretreated and pH adjusted. High-purity nitrogen gas with a purity of not less than 99.999% was bubbled into the homogeneous carboxymethyl cellulose aqueous solution obtained in step 1 at a flow rate of 0.5 L / min for 30 minutes. Subsequently, under nitrogen protection and stirring at 800 rpm, 0.2 g of dopamine hydrochloride was added in three portions through a solid feeding funnel, with each addition 5 minutes apart. Then, using an automatic potentiometric titrator, a 0.1 mol / L tris(hydroxymethyl)aminomethane (Tris) base solution was added dropwise to the system at a rate of 1 mL / min as a neutralizing agent until the pH of the system reached 8.0. The system temperature was monitored in real time during the addition to ensure that it did not exceed 40°C.

[0039] Then, a multi-stage composite reaction was carried out. The mixed system after pH adjustment in step 2 was transferred to a programmable temperature-controlled high-pressure reactor, sealed, and nitrogen gas was introduced to establish a nitrogen micro-positive pressure of 0.01 MPa. The low-temperature pre-adsorption stage reaction was carried out at a constant temperature of 30°C and a stirring rate of 500 r / min for 2 hours. During the reaction, in-situ infrared spectroscopy was used for real-time monitoring. The pre-adsorption stage was terminated when the peak intensity ratio of the hydroxyl characteristic peak of carboxymethyl cellulose to the amino characteristic peak of dopamine stabilized in the range of 0.3-0.5.

[0040] Subsequently, the reaction proceeded to a synergistic heating and pressurization phase. First, the reaction was carried out at 30℃ and 0.1MPa for 1 hour. Then, the system temperature was increased to 45℃ at a heating rate of 0.5℃ / min, while the pressure was simultaneously increased to 0.2MPa and the stirring rate to 900 r / min. During the reaction, real-time monitoring was performed using in-situ UV-Vis spectroscopy and a quartz crystal microbalance. The reaction was considered successful when the absorbance change rate at 280nm was no higher than 5% / h, or the mass growth rate measured by the quartz crystal microbalance stabilized at 0.5-1 μg / cm³. 2When the reaction is within the range of min, it is considered complete.

[0041] Finally, post-processing is performed. After the reaction is complete, the reaction product is subjected to gradient cooling and depressurization treatment, with the depressurization rate controlled at 0.1 MPa / h and the cooling rate controlled at 5℃ / h. The cooled product is then filtered using a hydrophilic / hydrophobic bilayer composite filter membrane with a pore size of 0.22 μm to obtain the composite dispersant.

[0042] Preparation of negative electrode slurry: 85g of graphite and 15g of acetylene black were added to 50mL of deionized water and premixed at a stirring rate of 800r / min for 30 minutes. Then, 3g of the prepared composite dispersant was added to the premix, the stirring rate was increased to 1000r / min, and dispersion was continued for 4 hours to finally obtain the negative electrode slurry.

[0043] Example 3:

[0044] Preparation of composite dispersants: First, a homogeneous carboxymethyl cellulose (CMC) aqueous solution was prepared. 100 ml of deionized water with a conductivity not exceeding 10 μS / cm was placed in a double-walled glass reactor. Under constant temperature water bath conditions of 40°C, 2 g of carboxymethyl cellulose (CMC) powder was slowly added at a stirring rate of 0.4 g / min at a stirring rate of 500 r / min. The degree of substitution of the CMC was 0.7-1.2, and the viscosity of its 1% aqueous solution was 1000-2500 mPa·s. After the addition was complete, ultrasonic-assisted dispersion at a power of 300 W and a frequency of 30 kHz was activated, while mechanical stirring was maintained at 500 r / min for 45 minutes until the powder was completely dissolved. The particle size distribution of the obtained solution was measured using a dynamic light scattering instrument, confirming that its coefficient of variation was not greater than 5%, thus obtaining a homogeneous CMC aqueous solution with a mass concentration of 2%.

[0045] Next, the reaction system was pretreated and pH adjusted. High-purity nitrogen gas with a purity of not less than 99.999% was bubbled into the homogeneous carboxymethyl cellulose aqueous solution obtained in step 1 at a flow rate of 0.5 L / min for 30 minutes. Subsequently, under nitrogen protection and stirring at 800 rpm, 0.2 g of dopamine hydrochloride was added in three portions through a solid feeding funnel, with each addition 5 minutes apart. Then, using an automatic potentiometric titrator, a 0.1 mol / L tris(hydroxymethyl)aminomethane (Tris) base solution was added dropwise to the system at a rate of 1 mL / min as a neutralizing agent until the pH of the system reached 8.0. The system temperature was monitored in real time during the addition to ensure that it did not exceed 40°C.

[0046] Then, a multi-stage composite reaction was carried out. The mixed system after pH adjustment in step 2 was transferred to a programmable temperature-controlled high-pressure reactor, sealed, and nitrogen gas was introduced to establish a nitrogen micro-positive pressure of 0.01 MPa. The low-temperature pre-adsorption stage reaction was carried out at a constant temperature of 30°C and a stirring rate of 500 r / min for 2 hours. During the reaction, in-situ infrared spectroscopy was used for real-time monitoring. The pre-adsorption stage was terminated when the peak intensity ratio of the hydroxyl characteristic peak of carboxymethyl cellulose to the amino characteristic peak of dopamine stabilized in the range of 0.3-0.5.

[0047] Subsequently, the reaction proceeded to a synergistic heating and pressurization phase. First, the reaction was carried out at 30℃ and 0.1MPa for 1 hour. Then, the system temperature was increased to 45℃ at a heating rate of 0.5℃ / min, while the pressure was simultaneously increased to 0.2MPa and the stirring rate to 900 r / min. During the reaction, real-time monitoring was performed using in-situ UV-Vis spectroscopy and a quartz crystal microbalance. The reaction was considered successful when the absorbance change rate at 280nm was no higher than 5% / h, or the mass growth rate measured by the quartz crystal microbalance stabilized at 0.5-1 μg / cm³. 2 When the reaction is within the range of min, it is considered complete.

[0048] Finally, post-processing was performed. After the reaction was completed, the reaction product was subjected to gradient cooling and depressurization treatment, with the depressurization rate controlled at 0.1 MPa / h and the cooling rate controlled at 5 °C / h. Finally, the cooled product was filtered using a hydrophilic / hydrophobic bilayer composite filter membrane with a pore size of 0.22 μm to obtain the composite dispersant.

[0049] Preparation of negative electrode slurry: 90g of graphite and 10g of acetylene black were added to 50mL of deionized water and premixed at a stirring rate of 800r / min for 30 minutes. Then, 2.5g of the prepared composite dispersant was added to the premix, and the stirring rate was increased to 1200r / min for continuous dispersion for 3.5 hours to finally obtain the negative electrode slurry.

[0050] Comparative Examples 1-2: Comparative Example 1: Compared to Example 1, the difference lies in that the dispersant used in the negative electrode slurry preparation step is a pure carboxymethyl cellulose (CMC) aqueous solution that has not been treated by the composite reaction step of this invention, wherein the solid content of CMC is the same as the amount of composite dispersant used in Example 1. All other conditions are the same as in Example 1.

[0051] Comparative Example 2: The difference from Example 1 is that the dispersant used is a physically mixed aqueous solution of carboxymethyl cellulose (CMC) and dopamine hydrochloride. Specifically, the same amount of CMC and dopamine hydrochloride as in Example 1 were directly dissolved in water, without pH adjustment or subsequent low-temperature pre-adsorption, temperature and pressure increases, or other multi-stage complex reactions. All other conditions were the same as in Example 1.

[0052] Test Example 1-3: Test Example 1: Negative electrode slurry stability test: To verify the effect of the composite dispersant prepared in this invention on the stability of the negative electrode slurry, static sedimentation experiments were conducted on five groups of negative electrode slurry samples prepared in Examples 1-3 and Comparative Examples 1-2.

[0053] Experimental steps: Take 50 mL of each of the five negative electrode slurries prepared in Examples 1-3 and Comparative Examples 1-2, and put them into clean, dry, sealed glass graduated cylinders of the same size and scale (100 mL each).

[0054] Record the initial total volume of each sample in the graduated cylinder and ensure that the liquid level is consistent.

[0055] Place all graduated cylinders vertically on a vibration-free horizontal experimental platform and let them stand at room temperature (25℃).

[0056] After standing for 24 hours and 48 hours respectively, the height of the transparent liquid layer (i.e., supernatant) separated from the slurry in each graduated cylinder was observed and recorded.

[0057] Experimental data: The table below records the supernatant height of each slurry sample at different settling time points.

[0058] Table 1. Height of supernatant after different standing times for each slurry sample

[0059] Results analysis: The experimental data in Table 1 show that the supernatant height of the negative electrode slurries prepared using the methods of Examples 1, 2, and 3 did not exceed 1.5 mm after standing for 48 hours. In contrast, the supernatant heights of the negative electrode slurries prepared using the methods of Comparative Examples 1 and 2 reached 24.1 mm and 20.5 mm, respectively, after the same standing time. This data indicates that the particle settling rate of the slurry prepared using the composite dispersant described in this invention is significantly lower than that of the slurry using pure carboxymethyl cellulose or its physical mixture with dopamine as a dispersant.

[0060] The reason for the above differences lies in the fact that this invention, through a multi-stage programmed composite reaction of carboxymethyl cellulose and dopamine in a weakly alkaline environment (pH 8.0-8.5), forms a specific molecular structure. In this structure, the regions formed by the self-polymerization of dopamine can be firmly anchored to the particle surfaces of the negative electrode active material and the conductive agent. Simultaneously, the long chains of carboxymethyl cellulose attached to them extend into the aqueous medium, forming an effective steric hindrance layer. This synergistic effect of strong surface adsorption and steric hindrance physically hinders the approach and aggregation of particles, thereby maintaining the uniformity and stability of the entire slurry system.

[0061] In contrast, the pure carboxymethyl cellulose molecules in Comparative Example 1 primarily adhere to the particle surface through weak physical adsorption. Their adsorption strength is insufficient, making them prone to desorption or reconstruction after prolonged standing, failing to form a durable and effective steric hindrance, thus leading to particle sedimentation. In Comparative Example 2, due to the lack of specific pH control and multi-stage complex reactions, dopamine and carboxymethyl cellulose merely coexist physically, failing to form the aforementioned composite structure with strong anchoring effect. Therefore, their improvement on slurry stability is limited, and the particles also exhibit significant sedimentation.

[0062] Test Example 2: Microscopic morphology observation of negative electrode slurry: To characterize the microstructure of the negative electrode slurry prepared by the method of the present invention, the negative electrode slurry sample prepared in Example 3 was observed by scanning electron microscopy (SEM).

[0063] Experimental steps: Take about 0.1 mL of the negative electrode slurry prepared in Example 3.

[0064] The slurry sample is evenly dripped onto the conductive adhesive surface that is pre-fixed on the sample stage.

[0065] The sample stage containing the slurry sample was placed in a vacuum drying oven and vacuum dried at 40°C for 6 hours to remove moisture from the slurry and solidify its microstructure.

[0066] The surface of the dried sample was observed using a scanning electron microscope, and images were acquired at the same magnification.

[0067] Results analysis: Please see Figure 2 It displays scanning electron microscope images of the negative electrode slurry prepared using Example 3. From Figure 2It can be clearly observed that larger flake-like graphite particles and smaller spherical acetylene black particles are interwoven, forming a homogeneous mixture. The acetylene black particles, in the form of single or small aggregates, are uniformly attached to and embedded in the surface of the graphite particles and in the gaps between the particles, forming a complete three-dimensional conductive network structure. No large-sized acetylene black aggregates or large areas of exposed graphite surface were observed throughout the entire field of view.

[0068] The aforementioned microstructure is due to the molecular structure of the composite dispersant used in Example 3. Through the multi-stage reaction described in this invention, dopamine polymerizes in situ on carboxymethyl cellulose segments, forming a structure capable of simultaneously generating strong physical adsorption on particle surfaces with different properties. A portion of this structure is effectively anchored to the surfaces of graphite and acetylene black particles, while another portion of the carboxymethyl cellulose segments constitutes physical steric hindrance between particles. This structure allows the conductive agent particles to be effectively deagglomerated and stably dispersed around the negative electrode active material particles, thereby forming a... Figure 2 The homogenized microstructure is shown.

[0069] Test Example 3: Battery electrochemical performance testing: To verify the actual impact of the negative electrode slurry prepared by the method described in this invention on the electrochemical performance of lithium-ion batteries, batteries were assembled using the negative electrode slurries prepared in Examples 1 and 3, and their cycle performance was tested.

[0070] Experimental steps: The negative electrode slurries prepared in Examples 1 and 3 were uniformly coated onto copper foil current collectors and then subjected to vacuum drying, rolling and other processes to produce negative electrode sheets with uniform areal loading and compaction density.

[0071] Two types of negative electrode sheets were used as working electrodes, lithium metal sheets were used as counter electrodes, and polypropylene microporous membranes were used as separators. The cells were assembled into CR2032 coin cells together with a standard carbonate electrolyte containing lithium hexafluorophosphate in a glove box filled with high-purity argon.

[0072] The assembled coin cells were subjected to electrochemical performance testing at room temperature (25°C). The test regime was as follows: charge-discharge cycles were performed at a constant current rate of 0.5C for a total of 500 cycles, and the capacity retention of each cell was recorded and calculated.

[0073] Results analysis: Please see Figure 3 The figure shows the capacity retention of batteries prepared using the slurries from Examples 1 and 3 as a function of cycle number. Examples 1 and 3 are... Figure 3Examples 1 and 3, as shown in the figure, demonstrate that batteries using the slurries of Examples 1 and 3 both exhibit high cycle stability. Specifically, the battery using the slurry of Example 3 retained 99.2% of its capacity after 100 cycles and maintained 97.2% after 500 cycles; the battery using the slurry of Example 1 retained 97.0% of its capacity after 100 cycles and 95.2% after 500 cycles. The data indicate that the capacity retention of Example 3 was consistently higher than that of Example 1 throughout the entire testing period.

[0074] This performance improvement is directly related to the microstructure inside the electrode, which stems from the specific mechanism of action of the composite dispersant used. The composite dispersant prepared by this invention through a multi-stage reaction has a molecular structure that ensures a highly uniform dispersion of the negative electrode active material and the conductive agent in the slurry. This uniformity is fully preserved in the final electrode coating, forming a continuous and efficient three-dimensional conductive network and ensuring a uniform migration path for lithium ions within the electrode bulk phase. This reduces the overall charge transfer resistance of the electrode and effectively suppresses localized polarization. Specifically, this homogeneous electrode microstructure constructed by the composite dispersant of this invention (its morphology can be seen in the image shown in Test Example 2) ensures that during the electrochemical reaction, the insertion and extraction of lithium ions and the conduction of electrons can proceed uniformly throughout the three-dimensional space of the entire electrode.

[0075] During long-term electrochemical cycling, a uniform electrode structure allows for a uniform distribution of current density across the entire active electrode surface, preventing the aggravation of side reactions caused by excessive local current, such as excessive electrolyte decomposition and unstable thickening of the solid electrolyte interphase (SEI) film. This reduces irreversible loss of active lithium ions and maintains the integrity of the electrode structure. In contrast, the heterogeneous electrode structure in Comparative Example 1, caused by particle agglomeration, leads to severe current density unevenness, accelerating the aforementioned degradation mechanism and resulting in a rapid decrease in battery capacity during cycling.

Claims

1. A slurry dispersion method based on carboxymethylcellulose complexed with dopamine, characterized in that, include: S1. Preparing a composite dispersant, wherein the step of preparing the composite dispersant includes: S11. Provide a homogeneous aqueous solution of carboxymethyl cellulose; S12. Add dopamine hydrochloride to the homogeneous carboxymethyl cellulose aqueous solution and adjust the pH of the system to 8.0-8.5 using a neutralizing agent to obtain a pH-adjusted mixed system, wherein the mass ratio of the carboxymethyl cellulose to the dopamine hydrochloride is (5-20):1; S13. The pH-adjusted mixture is subjected to a composite reaction at a temperature of 20-45°C for 2-12 hours to obtain the reaction product; S14. The reaction product is post-processed to obtain a composite dispersant; S2. Preparing a negative electrode slurry using the composite dispersant, wherein the step of preparing the negative electrode slurry includes: S21. The negative electrode active material and the conductive agent are added to deionized water for premixing to obtain a premixed solution, wherein the mass ratio of the negative electrode active material to the conductive agent is (80-95):(5-20). S22. The composite dispersant obtained in step S1 is added to the premixed liquid for final dispersion, thereby obtaining the negative electrode slurry.

2. The slurry dispersion method based on carboxymethyl cellulose and dopamine complexing according to claim 1, characterized by, In step S11, the preparation conditions for the homogeneous carboxymethyl cellulose aqueous solution include: In a double-walled glass reactor, carboxymethyl cellulose powder with a degree of substitution of 0.7-1.2 and a viscosity of 1% aqueous solution of 1000-2500 mPa·s was used. The carboxymethyl cellulose powder is added to deionized water with a conductivity ≤10μS / cm at 30-40℃, and the addition rate is controlled at 0.1-0.5g / min, while the initial stirring rate is controlled at 300-500r / min. After the addition is complete, disperse the homogeneous carboxymethyl cellulose aqueous solution for 30-60 minutes under mechanical stirring at 500-800 r / min and ultrasonic assistance at 200-500 W and 20-40 kHz to obtain a mass concentration of 0.5%-5%. The particle size distribution of the homogeneous carboxymethyl cellulose aqueous solution was determined using a dynamic light scattering instrument to ensure that the coefficient of variation of the particle size distribution was ≤5%.

3. The slurry dispersion method based on carboxymethyl cellulose and dopamine complexing according to claim 1, characterized by, In step S12, the specific operating conditions include: a. First, the homogeneous carboxymethyl cellulose aqueous solution is subjected to nitrogen deoxygenation treatment, wherein the nitrogen gas is high-purity nitrogen gas with a purity ≥99.999%, the flow rate is 0.5-1L / min, and the aeration time is 25-35 minutes; b. Then, in the solution treated in step a, under nitrogen protection and stirring at 800-1000 r / min, the dopamine hydrochloride is added in 2-5 portions with an interval of 3-10 minutes between each addition through a solid feeding funnel to obtain a mixture containing dopamine hydrochloride. c. Finally, using an automatic potentiometric titrator, a neutralizing agent is added dropwise to the mixture containing dopamine hydrochloride obtained in step b until the pH of the system reaches 8.0-8.

5. The neutralizing agent is a 0.05-0.15 mol / L tris(hydroxymethyl)aminomethane base solution or a 0.4-0.6 mol / L sodium hydroxide solution, and the dropping rate of the neutralizing agent is 0.5-2 mL / min. The system temperature is monitored in real time during the dropping process to ensure that it does not exceed 40°C.

4. The slurry dispersion method based on carboxymethyl cellulose and dopamine complexing according to claim 1, characterized by, In step S13, the specific procedure for the composite reaction includes: a. Low-temperature pre-adsorption stage: The pH-adjusted mixture was transferred to a programmable temperature-controlled high-pressure reactor. Under a nitrogen micro-positive pressure of 0.01-0.02 MPa, the temperature was controlled at 20-30℃ and the stirring rate at 500-800 r / min for 1.5-2.5 hours to obtain the pre-adsorbed product. The reaction was monitored in real time by an in-situ infrared spectrometer. When the peak intensity ratio of the hydroxyl characteristic peak of carboxymethyl cellulose to the amino characteristic peak of dopamine stabilized at 0.3-0.5, the pre-adsorption was determined to be complete. b. Synergistic reaction stage of heating and pressurization: The pre-adsorbed product obtained in step a is first reacted at 25-35℃ and 0.08-0.12MPa for 0.5-1.5 hours. Then, the temperature is raised to 40-50℃ at a heating rate of 0.3-0.7℃ / min, and the pressure is simultaneously increased to 0.18-0.22MPa, while the stirring rate is increased to 900-1100r / min. The reaction process is tracked in real time by in-situ UV-visible spectroscopy and quartz crystal microbalance, wherein the stable period of the reaction process is determined by at least one of the following: the absorbance change rate at 280 nm of the in-situ UV-visible spectroscopy is ≤5% / h, or the mass growth rate measured by the quartz crystal microbalance is stably at 0.5-1 μg / cm 2 ·min. • The reaction process is tracked in real time by in-situ UV-visible spectroscopy and quartz crystal microbalance, wherein the stable period of the reaction process is determined by at least one of the following: the absorbance change rate at 280 nm of the in-situ UV-visible spectroscopy is ≤5% / h, or the mass growth rate measured by the quartz crystal microbalance is stably at 0.5-1 μg / cm 2 ·min.

5. The slurry dispersion method based on carboxymethyl cellulose and dopamine complexing according to claim 1, characterized by, In step S14, the post-processing procedure includes: a. Gradient cooling and depressurization: The reaction product is subjected to cooling and depressurization treatment, with the depressurization rate controlled at 0.05MPa / h-0.1MPa / h and the cooling rate controlled at 2℃ / h-5℃ / h, so as to obtain the cooled reaction product. b. Filtration: The cooled reaction product obtained in step a is filtered using a 0.2-0.3 μm hydrophilic / hydrophobic bilayer composite filter membrane.

6. The slurry dispersion method based on carboxymethyl cellulose and dopamine complexing according to claim 1, characterized by, In step S21, the specific conditions for premixing include: The stirring speed is 500-1000 r / min, and the stirring time is 10-30 minutes.

7. The slurry dispersion method based on carboxymethyl cellulose and dopamine complexing according to claim 1, characterized by, In step S22, the specific conditions for the final dispersion include: The amount of the composite dispersant added is 0.5%-3% of the mass of the negative electrode active material, the stirring rate is 800-1500 r / min, the temperature is 20-40℃, and the stirring time is 2-6 hours.

8. The slurry dispersion method based on carboxymethyl cellulose and dopamine complexing according to claim 1, characterized by, In step S21, the negative electrode active material is at least one of graphite, silicon-based material, and lithium titanate.

9. The slurry dispersion method based on carboxymethyl cellulose and dopamine complexing according to claim 1, characterized by, In step S21, the conductive agent is at least one of superconducting carbon black, carbon nanotubes, and acetylene black.

10. The application of a negative electrode slurry prepared by the method of any one of claims 1-9 in a lithium-ion battery.

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