Uniformly dispersed and difficult-to-settle positive electrode slurry and preparation method thereof

Abstract

The invention discloses a uniformly dispersed and difficult-to-settle positive electrode slurry and a preparation method thereof. The method comprises the following steps: S1, putting a positive electrode active material, a conductive agent and a binder raw material into a vacuum drying oven for drying treatment; s2, adding the pretreated positive electrode active material, a conductive agent and a binder into a solvent, and uniformly stirring to prepare initial slurry with the solid content of 45-55 wt%; s3, carrying out rotation speed gradient ascending shear dispersion treatment on the initial slurry; s4, performing intermittent ultrasonic treatment on the slurry subjected to gradient shearing treatment in an ultrasonic disperser; s5, 0.3 wt%-0.8 wt% of an amphiphilic polymer surfactant is added into the slurry obtained after ultrasonic treatment; and S6, adding 0.1-0.5 wt% of a nano aluminum oxide anti-settling agent into the slurry. According to the invention, the problems of non-uniform dispersion and easy sedimentation of the existing positive electrode slurry can be effectively solved, and the quality and product consistency of the lithium ion battery are improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of battery material preparation, and in particular relates to a positive electrode slurry that is uniformly dispersed and not prone to sedimentation, and a preparation method thereof. Background Art

[0002] Lithium-ion batteries are widely used in consumer electronics, electric vehicles, and energy storage systems. Slurry preparation is a crucial step in the lithium battery manufacturing process. Slurry quality directly impacts the battery's electrochemical performance, production efficiency, and safety. In actual production, slurry sedimentation and large viscosity variations often occur, affecting battery consistency.

[0003] At present, the sedimentation problem of positive electrode slurry is mainly caused by the following reasons: 1) Unstable slurry water absorption: The water absorption of the slurry is an important factor affecting its stability. When the slurry absorbs too much water, its composition will change, thereby affecting its physical properties such as viscosity. In addition, water absorption will cause the solid particles in the slurry to agglomerate, thereby accelerating the sedimentation of the slurry. 2) Insufficient viscosity: The binder is an important component for maintaining the stability of the slurry. If the binder content is insufficient, the viscosity of the slurry will decrease, resulting in poor stability and easy sedimentation. 3) Poor dispersion effect: During the preparation process, if the solid particles cannot be fully dispersed in the medium, the dispersion effect of the slurry will be poor, which will affect its stability. The agglomeration and sedimentation of solid particles will lead to inconsistent battery performance and may even cause battery safety problems.

[0004] Existing solutions to these problems primarily include adjusting raw material selection, optimizing the mixing process, adjusting binder dosage, and controlling ambient moisture. However, these approaches often address the problem from a single perspective, lacking systematicity and synergy, and thus failing to fundamentally address the issues of slurry sedimentation and large viscosity variations. For example, simply increasing the stirring time can lead to increased temperatures, which in turn accelerates coagulation and sedimentation. Simply reducing the binder dosage can reduce the risk of coagulation, but this can compromise the electrode bond strength.

[0005] Therefore, there is an urgent need to develop a comprehensive method for preparing positive electrode slurry to solve the problems of uneven slurry dispersion and easy sedimentation, and to improve the quality and product consistency of lithium-ion batteries. Summary of the Invention

[0006] The purpose of the present invention is to provide a method for preparing a positive electrode slurry that is uniformly dispersed and not prone to sedimentation, in order to address the shortcomings of the existing technology and improve the quality and product consistency of lithium-ion batteries.

[0007] To achieve the above object, the present invention provides the following technical solutions:

[0008] A method for preparing a positive electrode slurry that is uniformly dispersed and not prone to sedimentation comprises the following steps:

[0009] S1. Raw material drying pretreatment: Place the positive electrode active material, conductive agent and binder raw materials in a vacuum drying oven for drying at a vacuum degree of -0.08~-0.12MPa, a temperature of 60~80℃, and a drying time of 8~12 hours;

[0010] S2. Slurry preparation: Add the pretreated positive electrode active material, conductive agent, and binder to a solvent in a mass ratio of 92-96:1-3:3-5, and stir evenly to prepare an initial slurry, wherein the solvent is N-methylpyrrolidone (NMP) and the solid content is 45-55wt%;

[0011] S3, gradient shear dispersion treatment: the initial slurry is stirred at 300-500 rpm for 15-20 minutes, at 600-800 rpm for 20-30 minutes, at 900-1100 rpm for 10-15 minutes, and finally at 1200-1500 rpm for 5-10 minutes;

[0012] S4, ultrasonic-assisted dispersion treatment: the slurry after gradient shear treatment is placed in an ultrasonic disperser with an ultrasonic power of 400-600 W and a frequency of 25-35 kHz. The ultrasonic treatment is performed intermittently for 30-60 minutes with an intermittent ratio of 3:1.

[0013] S5. Surfactant control: adding 0.3-0.8 wt% of an amphiphilic polymer surfactant having a hydrophilic-lipophilic balance (HLB) of 10-14 to the slurry after ultrasonic treatment;

[0014] S6. Add anti-settling agent: Add 0.1~0.5wt% of nano-alumina to the slurry. The particle size of nano-alumina is 10~50nm and the specific surface area is 100~150m² / g.

[0015] Preferably, in S1, the vacuum degree is released and restored every 2 hours during the drying process of the raw material, and each release time is 5 to 10 minutes to promote sufficient evaporation of moisture inside the raw material.

[0016] Preferably, during the gradient shear dispersion treatment in S3, the stirrer adopts a variable diameter stirring paddle, the ratio of the stirring paddle diameter to the container diameter is 0.7-0.8, and the distance between the bottom of the stirring paddle and the bottom of the container is 0.3-0.5 times the container diameter.

[0017] Preferably, the ultrasonic-assisted dispersion treatment in S4 is cooled by an ice-water bath to control the slurry temperature not to exceed 35° C., and the ultrasonic intermittent mode is 30 seconds of ultrasonication and 10 seconds of pause.

[0018] Preferably, the amphiphilic polymer surfactant is one or a mixture of polyvinyl pyrrolidone (PVP), polyethylene oxide (PEO), polyethylene glycol (PEG), polyvinyl alcohol (PVA) and sodium dodecyl sulfate (SDS).

[0019] Preferably, the positive electrode active material is one or a mixture of lithium nickel cobalt manganese oxide, lithium iron phosphate, and lithium cobalt oxide, the conductive agent is one or a mixture of conductive carbon black, graphene, and carbon nanotubes, and the binder is PVDF.

[0020] Preferably, the surface of the nano-alumina in S6 is modified with a silane coupling agent, the silane coupling agent is 3-aminopropyltriethoxysilane (KH550), and the modification method is: dispersing the nano-alumina in ethanol, adding the silane coupling agent, the mass ratio of which is 100:5~8, refluxing at 60~70°C for 4~6 hours, filtering, washing and drying to obtain modified nano-alumina.

[0021] Preferably, the nano-alumina in S6 is pre-dispersed with a small amount of NMP solvent before being added. The pre-dispersion treatment includes: mixing the nano-alumina and NMP in a mass ratio of 1:10-20, and treating with ultrasound for 30-60 minutes at a power of 200-300W and a frequency of 40-60kHz.

[0022] Preferably, step S7 is also included: slurry aging treatment, the slurry to which nano-alumina is added is subjected to vacuum degassing treatment at 25~35°C for 20~40 minutes, and the degassing pressure is -0.06~-0.09MPa, and then the slurry is allowed to stand and mature in a sealed container for 12~24 hours. During the aging process, dry nitrogen or argon is filled in the container, and the relative humidity is controlled below 5%.

[0023] Preferably, step S8 is also included: slurry performance evaluation, using a Brookfield viscometer to measure the viscosity difference between the top and bottom of the slurry after sedimentation for 24 hours, and controlling the difference to not more than 5%; using a laser particle size analyzer to measure the particle size distribution of solid phase particles in the slurry, D90≤10μm, D50≤5μm; measuring the thixotropic index of the slurry, and controlling it between 1.10 and 1.25 to ensure that the slurry has good anti-settling and coating properties.

[0024] In addition, the present invention also provides a positive electrode slurry, which is prepared by the method for preparing a positive electrode slurry with uniform dispersion and low sedimentation properties described in any of the above paragraphs.

[0025] Compared with the prior art, the present invention has at least the following beneficial effects:

[0026] 1) The present invention uses vacuum drying to pretreat the raw materials and promotes the full evaporation of internal moisture through periodic vacuum release, thus solving the problem of slurry instability caused by moisture introduced into the raw materials, and providing a dry and stable raw material foundation for subsequent slurry preparation;

[0027] 2) This invention innovatively introduces gradient shear dispersion technology. Through a multi-stage stirring process with different speeds, the particles in the slurry are gradually dispersed, avoiding the problems of local excessive shearing or insufficient dispersion that may be caused by traditional single-speed stirring, and achieving a more uniform dispersion effect.

[0028] 3) This invention combines ultrasonic-assisted dispersion with traditional mechanical stirring. The cavitation effect generated by ultrasound can effectively break up particle agglomerates. At the same time, intermittent ultrasound and ice-water bath cooling are used to avoid the local overheating and solvent volatilization problems that may be caused by continuous ultrasound, ensuring the stability of slurry performance.

[0029] 4) By precisely controlling the hydrophilic-lipophilic balance (HLB) value of the amphiphilic polymer surfactant within the range of 10-14, the present invention effectively regulates the surface properties of the active material particles, forming a stable dual protective layer of steric repulsion and electrostatic repulsion, significantly improving the dispersion stability of the slurry;

[0030] 5) This invention uniquely uses nano-alumina modified with a silane coupling agent as an anti-settling agent. Its high specific surface area and good compatibility enable it to form a network structure in the slurry, significantly improving the thixotropy and anti-settling properties of the slurry. After 24 hours of settling, the difference in top and bottom viscosity is controlled within 5%, which is far better than the difference of traditional slurries.

[0031] 6) The present invention combines slurry maturation with inert gas protection to allow the slurry components to fully interact with each other to reach a stable state, while avoiding the influence of ambient humidity on the slurry, further enhancing the long-term stability of the slurry, and maintaining stable and consistent performance of the slurry during the production process.

[0032] In summary, the positive electrode slurry preparation method provided by the present invention, through a multi-dimensional coordinated control strategy, from raw material pretreatment, dispersion process optimization to the rational application of surfactants and anti-settling agents, comprehensively solves the problems of uneven slurry dispersion and easy sedimentation, provides a high-quality slurry basis for lithium-ion battery production, and effectively improves the consistency and performance of the battery. DETAILED DESCRIPTION

[0033] The following will clearly and completely describe the technical solutions of the present invention in conjunction with specific embodiments. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0034] According to a first aspect of the present application, the present application provides a method for preparing a positive electrode slurry that is uniformly dispersed and not prone to sedimentation, comprising the following steps:

[0035] S1. Raw material drying pretreatment: Place the positive electrode active material, conductive agent and binder raw materials in a vacuum drying oven for drying at a vacuum degree of -0.08~-0.12MPa, a temperature of 60~80℃, and a drying time of 8~12 hours;

[0036] S2. Slurry preparation: Add the pretreated positive electrode active material, conductive agent, and binder to a solvent in a mass ratio of 92-96:1-3:3-5, and stir evenly to prepare an initial slurry, wherein the solvent is N-methylpyrrolidone (NMP) and the solid content is 45-55wt%;

[0037] S3, gradient shear dispersion treatment: the initial slurry is stirred at 300-500 rpm for 15-20 minutes, at 600-800 rpm for 20-30 minutes, at 900-1100 rpm for 10-15 minutes, and finally at 1200-1500 rpm for 5-10 minutes;

[0038] S4, ultrasonic-assisted dispersion treatment: the slurry after gradient shear treatment is placed in an ultrasonic disperser with an ultrasonic power of 400-600 W and a frequency of 25-35 kHz. The ultrasonic treatment is performed intermittently for 30-60 minutes with an intermittent ratio of 3:1.

[0039] S5. Surfactant control: adding 0.3-0.8 wt% of an amphiphilic polymer surfactant having a hydrophilic-lipophilic balance (HLB) of 10-14 to the slurry after ultrasonic treatment;

[0040] S6. Add anti-settling agent: Add 0.1~0.5wt% of nano-alumina to the slurry. The particle size of nano-alumina is 10~50nm and the specific surface area is 100~150m² / g.

[0041] In one embodiment of the present application, in S1, the vacuum degree is released and restored every 2 hours during the drying process of the raw material, and each release time is 5 to 10 minutes to promote the full evaporation of the water inside the raw material. By regularly releasing the vacuum degree, the water molecules inside the raw material can be more easily diffused to the surface and evaporated, thereby improving the drying efficiency, ensuring that the moisture content in the raw material is reduced to a minimum, and reducing the stability problems caused by moisture in the subsequent slurry preparation process. Experiments have shown that the use of a periodic vacuum release process can reduce the residual moisture content in the raw material to below 0.1% compared to continuous vacuum drying, significantly improving the stability of the slurry.

[0042] In one embodiment of the present application, the agitator for the gradient shear dispersion process in S3 employs a variable diameter impeller, wherein the ratio of the impeller diameter to the container diameter is 0.7 to 0.8, and the distance between the bottom of the impeller and the bottom of the container is 0.3 to 0.5 times the container diameter. The variable diameter impeller can generate a more complex flow field and stronger shear force, which is conducive to breaking up solid particle agglomerates. The appropriate impeller size and position can achieve optimal fluid circulation within the container, ensuring that all parts of the slurry are subjected to sufficient shear force, thereby improving dispersion uniformity.

[0043] Among them, the gradient shear dispersion process uses a four-stage stirring process with different speeds and has a specific mechanism and effect:

[0044] The first stage (300-500 rpm, 15-20 minutes): low-speed pre-dispersion stage, mainly to promote the initial wetting and mixing of materials, and avoid material splashing and agglomeration;

[0045] The second stage (600-800 rpm, 20-30 minutes): medium-speed dispersion stage, enhancing the uniform mixing of materials and initially destroying large agglomerates;

[0046] The third stage (900-1100 rpm, 10-15 minutes): high-speed dispersion stage, further refining the particles and improving the dispersion effect;

[0047] The fourth stage (1200~1500rpm, 5~10 minutes): ultra-high-speed final dispersion stage, which ultimately destroys tiny aggregates and forms a uniform and stable dispersion system.

[0048] Compared with traditional single-speed stirring, this gradient shear dispersion process can reduce the particle size D90 value from 15μm to below 10μm, greatly improving the dispersion uniformity.

[0049] In one embodiment of the present application, the ultrasonic-assisted dispersion treatment in S4 is cooled by an ice-water bath to control the slurry temperature to no more than 35°C, and the ultrasonic intermittent mode is 30 seconds of ultrasonication and 10 seconds of pause. During the ultrasonic process, the slurry temperature is monitored in real time by a thermocouple thermometer. When the temperature approaches 35°C, the pause time can be appropriately extended or the ultrasonic power can be reduced to ensure that the temperature is controlled within a predetermined range. Cooling with an ice-water bath can prevent the slurry from overheating during the ultrasonic process, resulting in solvent volatilization and changes in the slurry properties; the intermittent ultrasonic method can ensure sufficient ultrasonic energy input and give the slurry time to dissipate heat, preventing local overheating.

[0050] In one embodiment of the present application, the amphiphilic polymer surfactant is one or a mixture of polyvinyl pyrrolidone (PVP), polyethylene oxide (PEO), polyethylene glycol (PEG), polyvinyl alcohol (PVA), and sodium dodecyl sulfate (SDS). These surfactants have excellent hydrophilic and lipophilic groups and can be adsorbed on the surface of solid particles, forming steric barriers and electrostatic repulsion, effectively preventing particle agglomeration and sedimentation.

[0051] The surfactant HLB value range (10-14) was determined based on extensive experimental testing. When the HLB value is below 10, the surfactant is too lipophilic, making it difficult to fully disperse in the NMP solvent. When the HLB value is above 14, the surfactant is too hydrophilic, reducing its compatibility with the cathode material and organic solvents, making it difficult to effectively adsorb on the particle surface. Experimental results show that surfactants with an HLB value of 12-13 have the best stabilization effect on cathode slurries.

[0052] Preferably, the amphiphilic polymer surfactant is a mixture of polyvinylpyrrolidone (PVP) and sodium dodecyl sulfate (SDS), with the mass ratio of PVP to SDS being 2:1 to 1.5. The PVP and SDS composite dispersant system, through the synergistic effects of adsorption and electrostatic repulsion, forms a more stable dispersion system, effectively preventing aggregation of the active material and conductive agent. PVP primarily forms a protective layer on the particle surface through adsorption, while SDS enhances interparticle dispersion stability through electrostatic repulsion. The synergistic effect of the two significantly improves the stability of the slurry.

[0053] In one embodiment of the present application, the positive electrode active material is one or a mixture of lithium nickel cobalt manganese oxide, lithium iron phosphate, and lithium cobalt oxide; the conductive agent is one or a mixture of conductive carbon black, graphene, and carbon nanotubes; and the binder is PVDF. This combination is suitable for currently mainstream lithium-ion battery positive electrode material systems and exhibits excellent electrochemical performance and stability.

[0054] In one embodiment of the present application, the surface of the nano-alumina in S6 is modified with a silane coupling agent, 3-aminopropyltriethoxysilane (KH550). The modification method is as follows: the nano-alumina is dispersed in ethanol, the silane coupling agent is added at a mass ratio of 100:5-8, the reaction is refluxed at 60-70°C for 4-6 hours, and the modified nano-alumina is obtained by filtering, washing, and drying. Silane coupling agent modification can introduce organic functional groups onto the surface of the nano-alumina, enhancing its compatibility with the NMP solvent and slurry components, improving its dispersion stability in the slurry, and further enhancing its anti-settling effect.

[0055] Among them, the particle size of nano-alumina is directly related to the specific surface area. According to experimental tests, the correlation is as follows:

[0056]

[0057] Therefore, the particle size range of nano-alumina in the present invention (10-50 nm) and the specific surface area range (100-150 m² / g) have a good correspondence.

[0058] In one embodiment of the present application, the nano-alumina in S6 is pre-dispersed with a small amount of NMP solvent before being added. The pre-dispersion treatment includes mixing the nano-alumina with NMP at a mass ratio of 1:10-20 and ultrasonically treating for 30-60 minutes at a power of 200-300W and a frequency of 40-60kHz. The pre-dispersion treatment can first destroy the agglomeration between the nano-alumina and allow it to be fully dispersed in a small amount of solvent before being added to the slurry. This can avoid the problem of local agglomeration caused by direct addition and improve the dispersion uniformity of the nano-alumina in the slurry.

[0059] The pre-dispersion process uses relatively low ultrasonic power (200-300W) and relatively high frequency (40-60kHz) because nano-alumina particles are small and prone to agglomeration, requiring a higher frequency to provide a more intensive cavitation effect. At the same time, using relatively low power prevents localized high temperatures from causing excessive volatilization of the NMP solvent. Experiments have shown that this combination of parameters can reduce the size of secondary agglomerated nano-alumina particles from 200-300nm to below 50nm, significantly improving dispersion.

[0060] In one embodiment of the present application, step S7 is further included: slurry aging treatment, wherein the slurry to which nano-alumina has been added is subjected to vacuum degassing treatment at 25-35°C for 20-40 minutes at a degassing pressure of -0.06-0.09 MPa. The slurry is then allowed to stand and mature in a sealed container for 12-24 hours. During the aging process, the container is filled with dry nitrogen or argon, and the relative humidity is controlled below 5%. Vacuum degassing can remove bubbles in the slurry and prevent pinholes from appearing during the coating process. Controlling the ambient humidity during the aging process can prevent the slurry from absorbing water, ensuring that the slurry components fully interact and reach a stable state, thereby improving stability during subsequent use.

[0061] Compared to the matured slurry, the unmatured slurry exhibited significantly lower settling stability and coating uniformity. The aging process allowed the surfactant and anti-settling agent to fully function, forming a more stable dispersion. Slurry performance continued to improve with aging from 12 to 24 hours, but the improvement was less pronounced beyond 24 hours. Therefore, the optimal aging time range of 12 to 24 hours was selected.

[0062] In one embodiment of the present application, step S8 is also included: slurry performance evaluation, using a Brookfield viscometer to measure the difference in viscosity between the top and bottom of the slurry after 24 hours of sedimentation, controlling the difference to no more than 5%; using a laser particle size analyzer to measure the particle size distribution of the solid phase particles in the slurry, with D90 ≤ 10μm and D50 ≤ 5μm; and measuring the thixotropic index of the slurry and controlling it between 1.10 and 1.25 to ensure that the slurry has good anti-settling and coating properties. Through these rigorous performance index evaluations, it can be ensured that the slurry achieves the expected dispersion uniformity and anti-settling performance, providing quality assurance for subsequent battery manufacturing.

[0063] Among them, the thixotropic index of the slurry is an important parameter to characterize the rheological properties of the slurry, which is defined as the thixotropic index of the slurry at a low shear rate (usually 0.1s - ¹) and high shear rate (typically 100s - Thixotropic index is the ratio of the viscosity at 100 μm to the viscosity at 25°C (100 μm). Thixotropic index is measured using a rotational rheometer at 25°C using a parallel plate geometry with a 1mm gap, following a shear rate sweep from low to high to low. Slurries with a thixotropic index between 1.10 and 1.25 have both sufficient static structural strength to prevent settling and good flowability during coating, promoting the formation of a uniform coating.

[0064] According to the second aspect of the present application, the present application further provides a positive electrode slurry, which is prepared by the method for preparing a positive electrode slurry with uniform dispersion and low sedimentation properties described in any of the above paragraphs.

[0065] The implementation and advantages of this application will be further explained below with reference to specific embodiments.

[0066] Example 1

[0067] This embodiment provides a method for preparing a positive electrode slurry that is uniformly dispersed and not prone to sedimentation, comprising the following steps:

[0068] S1: Raw material drying pretreatment: NCM811 positive electrode active material, conductive carbon black and PVDF binder raw materials are placed in a vacuum drying oven for drying at a vacuum degree of -0.1 MPa and a temperature of 70°C for 10 hours. The vacuum is released and restored every 2 hours, with each release time of 8 minutes.

[0069] S2: Slurry preparation: pretreated NCM811, conductive carbon black and PVDF were added to NMP solvent in a mass ratio of 94:2:4 and stirred to obtain an initial slurry with a solid content of 50 wt%;

[0070] S3: Gradient shear dispersion treatment, using a variable diameter stirring paddle (the ratio of the stirring paddle diameter to the container diameter is 0.75, and the distance between the bottom of the stirring paddle and the bottom of the container is 0.4 times the container diameter). The initial slurry is stirred at 400 rpm for 18 minutes, 700 rpm for 25 minutes, 1000 rpm for 12 minutes, and finally at 1300 rpm for 8 minutes;

[0071] S4: Ultrasonic-assisted dispersion treatment: the slurry after gradient shear treatment was placed in an ultrasonic disperser and cooled in an ice-water bath to control the slurry temperature not exceeding 30°C. The ultrasonic power was 500W and the frequency was 30kHz. Intermittent ultrasonic treatment was performed for 45 minutes (30 seconds of ultrasonication each time and 10 seconds of pause);

[0072] S5: Surfactant control: add 0.5 wt% polyvinylpyrrolidone (PVP, HLB value 12) to the slurry after ultrasonic treatment and stir evenly;

[0073] S6: Addition of an anti-settling agent: 0.3 wt% of nano-alumina (particle size of 30 nm, specific surface area of ​​120 m² / g) was first mixed with NMP at a mass ratio of 1:15, and pre-dispersed using ultrasound (power of 250 W, frequency of 50 kHz) for 45 minutes. The mixture was then added to the slurry and stirred evenly. The surface of the nano-alumina was modified with a silane coupling agent, KH550: the nano-alumina was dispersed in ethanol, KH550 was added at a mass ratio of 100:6, and the mixture was refluxed at 65°C for 5 hours. The modified nano-alumina was obtained by filtration, washing, and drying.

[0074] S7: Slurry aging treatment: the slurry after adding nano-alumina is subjected to vacuum degassing treatment at 30°C for 30 minutes, with a degassing pressure of -0.08MPa. The slurry is then left to mature in a sealed container for 18 hours. During the aging process, dry nitrogen is filled into the container and the relative humidity is controlled at 3%.

[0075] S8: Slurry performance evaluation: The viscosity difference between the top and bottom of the slurry after 24 hours of sedimentation was measured by Brookfield viscometer, which was 3.2%; the particle size distribution of the solid phase particles in the slurry was measured by laser particle size analyzer, D90=8.5μm, D50=4.2μm; the thixotropic index of the slurry was 1.18.

[0076] Example 2

[0077] This embodiment provides a method for preparing a positive electrode slurry that is uniformly dispersed and not prone to sedimentation, comprising the following steps:

[0078] S1: Raw material drying pretreatment: LFP positive electrode active material, conductive carbon black, carbon nanotubes and PVDF binder raw materials are placed in a vacuum drying oven for drying. The vacuum degree is -0.09 MPa, the temperature is 65 ° C, and the drying time is 9 hours. The vacuum degree is released and restored every 2 hours, and the release time is 6 minutes each time.

[0079] S2: Slurry preparation: pretreated LFP, conductive carbon black, carbon nanotubes and PVDF were added to NMP solvent in a mass ratio of 93:1:1:5 and stirred to obtain an initial slurry with a solid content of 48 wt%;

[0080] S3: Gradient shear dispersion treatment, using a variable diameter stirring paddle (the ratio of the stirring paddle diameter to the container diameter is 0.72, and the distance between the bottom of the stirring paddle and the bottom of the container is 0.35 times the container diameter). The initial slurry is stirred at 350 rpm for 16 minutes, 650 rpm for 22 minutes, 950 rpm for 14 minutes, and finally at 1400 rpm for 6 minutes.

[0081] S4: Ultrasonic-assisted dispersion treatment: the slurry after gradient shear treatment was placed in an ultrasonic disperser and cooled in an ice-water bath to control the slurry temperature not exceeding 32°C. The ultrasonic power was 450W and the frequency was 28kHz. Intermittent ultrasonic treatment was performed for 40 minutes (30 seconds of ultrasonication and 10 seconds of pause each time).

[0082] S5: Surfactant control: add 0.4 wt% polyvinylpyrrolidone (PVP, HLB value 13) and 0.2 wt% sodium dodecyl sulfate (SDS) to the slurry after ultrasonic treatment and stir evenly;

[0083] S6: Addition of an anti-settling agent: 0.2 wt% of nano-alumina (particle size of 20 nm, specific surface area of ​​130 m² / g) was first mixed with NMP at a mass ratio of 1:18, and pre-dispersed using ultrasound (power of 280 W, frequency of 55 kHz) for 50 minutes. The mixture was then added to the slurry and stirred evenly. The surface of the nano-alumina was modified with a silane coupling agent KH550: the nano-alumina was dispersed in ethanol, KH550 was added at a mass ratio of 100:7, and the mixture was refluxed at 68°C for 5.5 hours. The modified nano-alumina was obtained by filtration, washing, and drying.

[0084] S7: Slurry aging treatment: the slurry after adding nano-alumina is subjected to vacuum degassing treatment at 28°C for 25 minutes, with a degassing pressure of -0.07MPa. The slurry is then left to mature in a sealed container for 16 hours. During the aging process, dry argon is filled into the container and the relative humidity is controlled at 4%.

[0085] S8: Evaluation of slurry performance: The viscosity difference between the top and bottom of the slurry after 24 hours of sedimentation was measured by Brookfield viscometer, which was 2.8%; the particle size distribution of the solid phase particles in the slurry was measured by laser particle size analyzer, D90=7.8μm, D50=3.9μm; the thixotropic index of the slurry was 1.20.

[0086] Example 3

[0087] This embodiment provides a method for preparing a positive electrode slurry that is uniformly dispersed and not prone to sedimentation, comprising the following steps:

[0088] S1: Raw material drying pretreatment: NCM523 positive electrode active material, conductive carbon black, graphene and PVDF binder raw materials are placed in a vacuum drying oven for drying at a vacuum degree of -0.11 MPa and a temperature of 75°C for 12 hours. The vacuum is released and restored every 2 hours, and the release time is 10 minutes each time.

[0089] S2: Slurry preparation: pretreated NCM523, conductive carbon black, graphene and PVDF were added to NMP solvent in a mass ratio of 95:1:1:3 and stirred to obtain an initial slurry with a solid content of 52 wt%.

[0090] S3: Gradient shear dispersion treatment, using a variable diameter stirring paddle (the ratio of the stirring paddle diameter to the container diameter is 0.78, and the distance between the bottom of the stirring paddle and the bottom of the container is 0.45 times the container diameter). The initial slurry is stirred at 450 rpm for 20 minutes, 750 rpm for 28 minutes, 1050 rpm for 15 minutes, and finally at 1450 rpm for 10 minutes;

[0091] S4: Ultrasonic-assisted dispersion treatment: the slurry after gradient shear treatment was placed in an ultrasonic disperser and cooled in an ice-water bath to control the slurry temperature not exceeding 35°C. The ultrasonic power was 550W and the frequency was 32kHz. Intermittent ultrasonic treatment was performed for 60 minutes (30 seconds of ultrasonication and 10 seconds of pause each time).

[0092] S5: Surfactant control: 0.6 wt% polyethylene oxide (PEO, HLB value 14) and 0.2 wt% polyvinyl alcohol (PVA) were added to the slurry after ultrasonic treatment and stirred evenly;

[0093] S6: Addition of an anti-settling agent: 0.4 wt% of nano-alumina (particle size of 15 nm, specific surface area of ​​145 m² / g) was first mixed with NMP at a mass ratio of 1:12, and pre-dispersed using ultrasound (power of 300 W, frequency of 60 kHz) for 60 minutes. The mixture was then added to the slurry and stirred evenly. The surface of the nano-alumina was modified with a silane coupling agent KH550: the nano-alumina was dispersed in ethanol, KH550 was added at a mass ratio of 100:8, and the mixture was refluxed at 70°C for 6 hours. The modified nano-alumina was obtained by filtration, washing, and drying.

[0094] S7: Slurry aging treatment: the slurry after adding nano-alumina is subjected to vacuum degassing treatment at 32°C for 35 minutes, with a degassing pressure of -0.09MPa. The slurry is then left to mature in a sealed container for 24 hours. During the aging process, dry nitrogen is filled into the container and the relative humidity is controlled at 2%.

[0095] S8: Slurry performance evaluation: the viscosity difference between the top and bottom of the slurry after 24 hours of sedimentation was measured by Brookfield viscometer, which was 2.5%; the particle size distribution of the solid phase particles in the slurry was measured by laser particle size analyzer, D90=7.2μm, D50=3.5μm; the thixotropic index of the slurry was 1.23.

[0096] Comparative Example 1

[0097] The method for preparing a positive electrode slurry provided in this comparative example comprises the following steps:

[0098] S1: Raw material pretreatment: NCM811 positive electrode active material, conductive carbon black and PVDF binder raw materials are placed in an oven for normal pressure drying at 100°C for 4 hours;

[0099] S2: Slurry preparation: pretreated NCM811, conductive carbon black and PVDF were added to NMP solvent in a mass ratio of 94:2:4 and stirred to obtain an initial slurry with a solid content of 50 wt%;

[0100] S3: Conventional stirring and dispersion treatment, the initial slurry was stirred at a constant speed of 800 rpm for 60 minutes;

[0101] S4: no ultrasound-assisted dispersion treatment;

[0102] S5: no surfactant added;

[0103] S6: no anti-settling agent added;

[0104] S7: Simple degassing treatment of the slurry: vacuum degassing the slurry at room temperature for 15 minutes and then use it directly;

[0105] S8: Evaluation of slurry performance: The viscosity difference between the top and bottom of the slurry after 24 hours of sedimentation was measured by Brookfield viscometer, which was 18.5%; the particle size distribution of the solid phase particles in the slurry was measured by laser particle size analyzer, D90=15.3μm, D50=8.7μm; the thixotropic index of the slurry was 1.05.

[0106] That is, in Comparative Example 1, conventional drying and stirring methods were used without using ultrasonic-assisted dispersion, surfactants, and anti-settling agents. The slurry stability and dispersion uniformity were poor, and sedimentation was severe.

[0107] Comparative Example 2

[0108] The method for preparing a positive electrode slurry provided in this comparative example comprises the following steps:

[0109] S1: Raw material pretreatment: LFP positive electrode active material, conductive carbon black and PVDF binder raw materials are placed in a vacuum drying oven for drying at a vacuum degree of -0.05 MPa, a temperature of 60°C, and a drying time of 6 hours;

[0110] S2: Slurry preparation: pretreated LFP, conductive carbon black and PVDF were added to NMP solvent in a mass ratio of 93:2:5 and stirred to obtain an initial slurry with a solid content of 48 wt%.

[0111] S3: Conventional stirring and dispersion treatment, the initial slurry was stirred at a constant speed of 600 rpm for 30 minutes, and then at a constant speed of 1000 rpm for 30 minutes;

[0112] S4: no ultrasound-assisted dispersion treatment;

[0113] S5: Add 0.5 wt% of a common surfactant (sodium dodecylbenzene sulfonate) to the slurry and stir evenly;

[0114] S6: no anti-settling agent added;

[0115] S7: simple aging treatment of the slurry, allowing the slurry to stand and mature at room temperature for 8 hours;

[0116] S8: Evaluation of slurry performance: The viscosity difference between the top and bottom of the slurry after 24 hours of sedimentation was measured by Brookfield viscometer, which was 12.3%; the particle size distribution of the solid phase particles in the slurry was measured by laser particle size analyzer, D90=13.5μm, D50=7.2μm; the thixotropic index of the slurry was 1.08.

[0117] Among them, Comparative Example 2 uses a simple dual-speed stirring process and a single surfactant, which is an improvement compared to Comparative Example 1. However, due to the lack of ultrasonic-assisted dispersion and anti-settling agent, the slurry still has obvious sedimentation problems and uneven dispersion.

[0118] Comparative Example 3

[0119] The method for preparing a positive electrode slurry provided in this comparative example comprises the following steps:

[0120] S1: Raw material pretreatment: NCM523 positive electrode active material, conductive carbon black and PVDF binder raw materials are placed in a vacuum drying oven for drying at a vacuum degree of -0.08 MPa, a temperature of 70°C, and a drying time of 8 hours;

[0121] S2: Slurry preparation: pretreated NCM523, conductive carbon black and PVDF were added to NMP solvent in a mass ratio of 95:1:4 and stirred to obtain an initial slurry with a solid content of 52 wt%.

[0122] S3: Conventional stirring and dispersion treatment, stirring the initial slurry at a constant speed of 1200 rpm for 60 minutes;

[0123] S4: Ultrasonic-assisted dispersion treatment: the stirred slurry is placed in an ultrasonic disperser with an ultrasonic power of 300 W and a frequency of 20 kHz for 20 minutes;

[0124] S5: no surfactant added;

[0125] S6: Add 0.8 wt% of common silica thickener (without surface modification) to the slurry and stir evenly;

[0126] S7: Simple aging treatment of the slurry: vacuum degassing the slurry at room temperature for 10 minutes, and then standing and aging for 6 hours;

[0127] S8: Evaluation of slurry performance: The viscosity difference between the top and bottom of the slurry after 24 hours of sedimentation was measured by Brookfield viscometer, which was 9.7%; the particle size distribution of the solid phase particles in the slurry was measured by laser particle size analyzer, D90=12.1μm, D50=6.5μm; the thixotropic index of the slurry was 1.12.

[0128] Among them, this comparative example represents a process using partially improved technology. Although ultrasonic dispersion and thickener are used, the slurry temperature is too high due to the lack of cooling measures, and the thickener used has not been surface-modified, so the dispersion effect is limited.

[0129] The slurries prepared in the above examples and comparative examples were respectively coated on aluminum foil to prepare electrodes, which were then assembled into 2032 button cells. The electrolyte was a 1 mol / L LiPF6 EC / DMC / EMC (volume ratio 1:1:1) solution, and the cells were assembled in an argon atmosphere glove box.

[0130] The following performance tests were performed on the electrodes and batteries prepared in the above examples and comparative examples, respectively. The test results are shown in Tables 1 and 2.

[0131] 1. Electrode Surface Uniformity Evaluation Method: An X-ray fluorescence (XRF) analyzer is used to measure the uniformity of the active material distribution in the electrode coating. Twenty-five measurement points are evenly distributed within a 10 cm x 10 cm area, and the relative standard deviation (RSD) of the active material weight percentage is calculated. The uniformity score is (1-RSD) x 10, with a maximum score of 10.

[0132] 2. Pole bonding strength test method: According to GB / T 2792-2014 standard, a 90° peel strength tester is used to measure the bonding strength between the coating and the substrate. The peel speed is 100 mm / min. Each sample is tested 5 times and the average value is taken.

[0133] 3. Battery Initial Charge and Discharge Efficiency Test Method: Using a Xinwei battery test system, perform the initial charge and discharge at a 0.1C rate at 25°C to measure the initial charge and discharge efficiency. Initial charge and discharge efficiency (%) = (initial discharge capacity / initial charge capacity) × 100%.

[0134] 4. Battery Cycle Performance Test Method: Using a Xinwei battery test system, charge and discharge the battery 300 times at a 1C rate at 25°C, and measure capacity retention. Capacity retention (%) = (discharge capacity after 300 cycles / initial discharge capacity) × 100%.

[0135] 5. Battery rate performance test method: Using the Xinwei battery test system, discharge at 0.5C, 1C, 2C, 5C, and 10C rates at 25°C, and measure the percentage of discharge capacity at each rate relative to the discharge capacity at 0.5C.

[0136] 6. Self-discharge rate test method: After fully charging the battery, store it at 25°C for 30 days and measure the changes in voltage and capacity. Self-discharge rate (%) = (initial capacity - capacity after storage) / initial capacity × 100%.

[0137] Table 1 Slurry performance test results

[0138]

[0139] Table 2 Battery performance test results

[0140]

[0141] The test results of Table 1 and Table 2 are analyzed as follows:

[0142] 1. Comparative analysis between the embodiment and the comparative example:

[0143] (1) Sedimentation Stability: After 24 hours of sedimentation, the top and bottom viscosity differences of the slurries of Examples 1-3 were all controlled within 3.2%, while the viscosity differences of Comparative Examples 1-3 were 18.5%, 12.3%, and 9.7%, respectively, significantly higher than those of the Examples. This indicates that the present invention effectively suppresses the sedimentation problem of the slurry through multi-dimensional coordinated regulation, especially through the synergistic effect of surfactants and modified nano-alumina.

[0144] (2) Particle Size Distribution: The D90 values ​​of Examples 1-3 were all less than 8.5 μm, and the D50 values ​​were all less than 4.2 μm, while the particle sizes of Comparative Examples 1-3 were significantly larger. This indicates that the combined gradient shear dispersion and ultrasound-assisted dispersion method of the present invention can more effectively break up particle agglomerates and achieve a more refined dispersion effect.

[0145] (3) Thixotropic Index: The thixotropic index of Examples 1-3 ranged from 1.18 to 1.23, which is within the ideal range (1.10-1.25), while the thixotropic index of the comparative example was lower. Appropriate thixotropic properties ensure that the slurry has sufficient structural strength to prevent sedimentation in a static state and maintains good fluidity under shear forces during the coating process.

[0146] (4) Pole Surface Uniformity: The pole piece surface uniformity scores for Examples 1-3 were all above 9.3 points, while those for Comparative Examples 1-3 were all below 8.1 points. This difference directly reflects the impact of slurry dispersion uniformity on the quality of the coated pole piece, demonstrating the significant effect of the method of the present invention on improving pole piece uniformity.

[0147] (5) Battery Performance: Examples 1-3 significantly outperformed Comparative Examples 1-3 in key battery performance indicators, including initial charge and discharge efficiency, cycle performance, rate performance, and self-discharge rate. The advantages of the Examples were particularly pronounced in high-rate (10C) discharge performance, fully demonstrating the direct impact of slurry quality on battery performance.

[0148] 2. Comparative analysis between various examples:

[0149] (1) Examples 2 and 3 outperformed Example 1 in many aspects, particularly in terms of sedimentation stability, particle size distribution, and battery cycling performance. This is primarily attributed to the use of more complex conductive agent combinations (carbon nanotubes, graphene) and surfactant combinations (PVP+SDS, PEO+PVA) in Examples 2 and 3, which provided more effective dispersion and stabilization.

[0150] (2) Example 3 showed the best sedimentation stability (viscosity difference of only 2.5%), which may be related to the use of the finest nano-alumina (15 nm), the highest ultrasonic power (550 W), and the longest aging time (24 hours). This combination of factors resulted in the slurry achieving the best dispersion and structural stability.

[0151] (3) The LFP material system (Example 2) showed the best cycling performance (92.3%), which is related to the good structural stability of the LFP material itself. However, through the preparation method of the present invention, its dispersibility and sedimentation stability were also significantly improved, further enhancing the cycling performance of the battery.

[0152] 3. Analysis of the effects of each process step:

[0153] (1) Raw material drying pretreatment: By comparing Example 1 and Comparative Example 1, it can be seen that vacuum drying pretreatment with periodic vacuum release (Example 1) can more thoroughly remove moisture from the raw materials than simple atmospheric pressure drying (Comparative Example 1), thus avoiding the instability problem of slurry caused by moisture at the source. In Comparative Example 1, due to residual moisture in the raw materials, the slurry sedimented severely (viscosity difference of 18.5%).

[0154] (2) Gradient shear dispersion: Compared with the dual-speed stirring of Comparative Example 2 and the constant-speed stirring of Comparative Example 3, the four-stage gradient shear dispersion process employed in Examples 1-3 more effectively disperses particles, resulting in a finer dispersion (smaller D90 and D50 values). The gradient shear process begins with uniform dispersion at a low speed and then breaks up agglomerates at a high speed, thus avoiding the potential for localized overshearing that can be caused by direct high-speed stirring.

[0155] (3) Ultrasonic-assisted dispersion: Comparison of Example 1 and Comparative Example 2 (without ultrasound) shows that ultrasound-assisted dispersion significantly improves the dispersion effect. The intermittent ultrasound (30 seconds of ultrasound followed by a 10-second pause) and ice-water cooling used in Example 1, compared to the continuous ultrasound used in Comparative Example 3, more effectively avoids local overheating and maintains stable slurry properties.

[0156] (4) Synergistic Effect of Surfactant and Anti-settling Agent: Examples 1-3 employed a design that employed the synergistic effect of an amphiphilic polymer surfactant and nano-alumina modified with a silane coupling agent, forming a dual stabilization mechanism. Compared to Comparative Example 2 (using only a conventional surfactant) and Comparative Example 3 (using an unmodified conventional thickener), the settling stability of the examples was improved several times. The introduction of the modified nano-alumina not only provided network structural support but also, through synergistic action with the surfactant, formed a more effective steric repulsion and spatial network structure, significantly enhancing the anti-settling properties of the slurry.

[0157] (5) Slurry maturation and protection: Compared with the simple treatment of Comparative Examples 1-3, the method of combining vacuum degassing with inert gas protection maturation adopted in Examples 1-3 enables the various components in the slurry to fully interact with each other and adjust their structures, while avoiding the influence of ambient humidity, further enhancing the long-term stability of the slurry.

[0158] 4. Analysis of the battery performance improvement mechanism:

[0159] (1) Improved initial charge and discharge efficiency: The initial charge and discharge efficiency of Examples 1-3 (90.5%-91.8%) was significantly higher than that of Comparative Examples 1-3 (85.3%-88.5%). This is primarily because the slurry prepared by the present invention has a more uniform dispersion, allowing for more complete contact between the active material and the conductive agent, forming a more complete conductive network, reducing the "dead corner" area in the electrode, and reducing the initial irreversible capacity loss.

[0160] (2) Improved Cycling Performance: The capacity retention rates of Examples 1-3 after 300 cycles (88.7%-92.3%) were much higher than those of Comparative Examples 1-3 (79.2%-85.1%). This is because the electrode structure formed by the slurry prepared by the present invention is more uniform and dense, and the bonding strength is higher (8.7-9.2 N / cm vs. 6.5-7.8 N / cm). This can better maintain the stability of the electrode structure during long-term cycling, reducing the risk of active material shedding and electrode structure collapse.

[0161] (3) Outstanding rate performance: The capacity retention rates of Examples 1-3 at a high rate of 10C (82.5%-85.2%) were significantly higher than those of Comparative Examples 1-3 (65.3%-73.2%). This difference is primarily due to the smaller particle size distribution and more uniform dispersion of the slurry prepared by the method of the present invention, resulting in electrodes with higher conductivity and ion transport efficiency, particularly exhibiting superior performance at high rate conditions.

[0162] (4) Reduced Self-Discharge Rate: The 30-day self-discharge rates of Examples 1-3 (2.1%-2.3%) were significantly lower than those of Comparative Examples 1-3 (3.9%-5.8%). This indicates that the slurry prepared in the present invention forms a more stable electrode structure, a more uniform electrode / electrolyte interface, reduces interfacial side reactions, and improves battery storage stability.

[0163] In summary, the present invention successfully addresses the issues of uneven dispersion and sedimentation in lithium-ion battery cathode slurries through a multi-dimensional, coordinated control strategy involving raw material drying pretreatment, gradient shear dispersion, ultrasonic-assisted dispersion, surfactant regulation, and the addition of a modified nano-alumina anti-settling agent. The prepared slurry exhibits excellent dispersion uniformity and anti-settling properties, and the resulting batteries demonstrate significant advantages in key metrics such as initial charge and discharge efficiency, cycle stability, rate capability, and self-discharge rate. This provides a high-quality slurry foundation for lithium-ion battery production, effectively improving battery consistency and performance.

[0164] Based on the disclosure and teachings of the above description, those skilled in the art will be able to make changes and modifications to the above embodiments. Therefore, the present invention is not limited to the above specific embodiments. Any obvious improvements, substitutions, or modifications made by those skilled in the art based on the present invention fall within the scope of protection of the present invention. In addition, although certain specific terms are used in this description, these terms are only for convenience of description and do not constitute any limitation to the present invention.

Claims

1. A method for preparing a positive electrode slurry that is uniformly dispersed and not prone to sedimentation, characterized in that: The following steps are involved: S1. Raw material drying pretreatment: Place the positive electrode active material, conductive agent and binder raw materials in a vacuum drying oven for drying at a vacuum degree of -0.08~-0.12MPa, a temperature of 60~80℃, and a drying time of 8~12 hours; S2. Slurry preparation: adding the pretreated positive electrode active material, conductive agent and binder to a solvent in a mass ratio of 92-96:1-3:3-5 and stirring evenly to prepare an initial slurry, wherein the solvent is N-methylpyrrolidone and the solid content is 45-55wt%; S3, gradient shear dispersion treatment: the initial slurry is stirred at 300-500 rpm for 15-20 minutes, at 600-800 rpm for 20-30 minutes, at 900-1100 rpm for 10-15 minutes, and finally at 1200-1500 rpm for 5-10 minutes; S4, ultrasonic-assisted dispersion treatment: the slurry after gradient shear treatment is placed in an ultrasonic disperser with an ultrasonic power of 400-600 W and a frequency of 25-35 kHz. The ultrasonic treatment is performed intermittently for 30-60 minutes with an intermittent ratio of 3:

1. S5. Surfactant control: adding 0.3-0.8 wt% of an amphiphilic polymer surfactant to the slurry after ultrasonic treatment, wherein the hydrophilic-lipophilic balance value of the surfactant is 10-14; S6. Add anti-settling agent: Add 0.1~0.5wt% of nano-alumina to the slurry. The particle size of nano-alumina is 10~50nm and the specific surface area is 100~150m² / g.

2. The method for preparing a positive electrode slurry with uniform dispersion and low sedimentation according to claim 1, characterized in that: In S1, the vacuum degree is released and restored every 2 hours during the drying process of the raw material, and each release time is 5 to 10 minutes to promote the full evaporation of water inside the raw material.

3. The method for preparing a positive electrode slurry with uniform dispersion and low sedimentation properties according to claim 1, characterized in that: During the gradient shear dispersion treatment in S3, the stirrer adopts a variable diameter stirring paddle, the ratio of the stirring paddle diameter to the container diameter is 0.7-0.8, and the distance between the bottom of the stirring paddle and the bottom of the container is 0.3-0.5 times the container diameter.

4. The method for preparing a positive electrode slurry with uniform dispersion and low sedimentation properties according to claim 1, characterized in that: The ultrasonic-assisted dispersion treatment in S4 is cooled by an ice-water bath to control the slurry temperature not to exceed 35° C., and the ultrasonic intermittent mode is 30 seconds of ultrasonication and 10 seconds of pause.

5. The method for preparing a positive electrode slurry with uniform dispersion and low sedimentation properties according to claim 1, characterized in that: The amphiphilic polymer surfactant is one or a mixture of polyvinyl pyrrolidone, polyethylene oxide, polyethylene glycol, polyvinyl alcohol and sodium lauryl sulfate; The positive electrode active material is one or a mixture of lithium nickel cobalt manganese oxide, lithium iron phosphate, and lithium cobalt oxide; the conductive agent is one or a mixture of conductive carbon black, graphene, and carbon nanotubes; and the binder is PVDF.

6. The method for preparing a positive electrode slurry with uniform dispersion and low sedimentation properties according to claim 1, characterized in that: The surface of the nano-alumina in S6 is modified by a silane coupling agent, wherein the silane coupling agent is 3-aminopropyltriethoxysilane. The modification method is as follows: dispersing the nano-alumina in ethanol, adding the silane coupling agent at a mass ratio of 100:5~8, refluxing at 60~70°C for 4~6 hours, filtering, washing and drying to obtain modified nano-alumina.

7. The method for preparing a positive electrode slurry with uniform dispersion and low sedimentation properties according to claim 1, characterized in that: Before adding the nano-alumina in S6, it is pre-dispersed with a small amount of NMP solvent. The pre-dispersion treatment includes: mixing the nano-alumina and NMP at a mass ratio of 1:10-20, and using ultrasonic treatment for 30-60 minutes with a power of 200-300W and a frequency of 40-60kHz.

8. The method for preparing a positive electrode slurry with uniform dispersion and low sedimentation properties according to claim 1, characterized in that: The method also includes step S7: slurry aging treatment, in which the slurry to which nano-alumina has been added is subjected to vacuum degassing treatment at 25-35°C for 20-40 minutes, and the degassing pressure is -0.06-0.09 MPa. The slurry is then allowed to stand and mature in a sealed container for 12-24 hours. During the aging process, dry nitrogen or argon is filled into the container, and the relative humidity is controlled below 5%.

9. The method for preparing a positive electrode slurry with uniform dispersion and low sedimentation properties according to claim 1, characterized in that: It also includes step S8: slurry performance evaluation, using a Brookfield viscometer to measure the viscosity difference between the top and bottom of the slurry after 24 hours of sedimentation, and controlling the difference to no more than 5%; using a laser particle size analyzer to measure the particle size distribution of solid phase particles in the slurry, D90≤10μm, D50≤5μm; measuring the thixotropic index of the slurry, and controlling it between 1.10 and 1.25 to ensure that the slurry has good anti-settling and coating properties.

10. A positive electrode slurry that is uniformly dispersed and not prone to sedimentation, characterized in that: The positive electrode slurry is prepared by the method for preparing the positive electrode slurry with uniform dispersion and low sedimentation properties according to any one of claims 1 to 9.

Images