Preparation method for inhibiting generation of aggregate particles on surface of positive electrode and positive electrode

Abstract

The invention discloses a preparation method for inhibiting aggregate particles from being generated on the surface of a positive electrode and the positive electrode. The method comprises the following steps: S1, respectively carrying out vacuum drying treatment on a positive electrode active material, a conductive agent and a binder; s2, the pretreated materials are put into a stirring tank with a pulse type vortex generator according to a preset proportion, and meanwhile the stirring temperature is controlled to range from 15 DEG C to 25 DEG C through a temperature control system; s3, guiding the prepared slurry into an ultrasonic dispersion device for dispersion; s4, enabling the treated slurry to sequentially pass through filtering devices with the filtering precision of 5 microns, 2 microns and 1 micron; and S5, uniformly stirring the filtered slurry under the protection of inert gas, and treating the slurry through a shearing device. Compared with the prior art, formation of aggregate particles on the surface of the positive electrode can be effectively inhibited, and the pole piece quality and the battery performance are improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of battery preparation, and in particular relates to a preparation method for suppressing the generation of agglomerated particles on the surface of a positive electrode and a positive electrode. Background Art

[0002] Lithium-ion batteries, currently the most important energy storage device, are widely used in consumer electronics, electric vehicles, and energy storage systems. During the manufacturing process of lithium-ion batteries, the quality of the cathode electrode directly impacts battery performance and safety. Agglomerate particle defects on the cathode electrode surface are a common problem in lithium-ion battery production. These agglomerates not only affect the battery's electrochemical performance but can also pose safety risks.

[0003] In the prior art, the formation of agglomerate particles on the surface of the positive electrode plate is mainly due to the following reasons: first, uneven stirring of the slurry leads to insufficient dispersion of the conductive agent and the binder, forming agglomerates; second, metal powder contamination during the production process will form agglomerates with metal powder as the core; third, excessively high ambient humidity will cause local colloidization of the slurry, and eventually form agglomerate particles; in addition, the properties of the material itself and the state of the production equipment will also affect the formation of agglomerates.

[0004] Currently, methods for suppressing the formation of aggregate particles on the cathode surface primarily include optimizing the slurry mixing process to improve material dispersion; controlling metal powder contamination; adjusting environmental conditions to control humidity; and improving filtration processes. However, these methods often focus on optimizing a single factor, lacking systematic and synergistic approaches, and thus fail to fundamentally address the aggregate particle problem. In particular, the aggregate particle problem becomes more complex and severe during the production of high-energy-density batteries, as electrode thickness increases and material ratios adjust.

[0005] Therefore, there is an urgent need to develop a systematic and multi-faceted preparation method that can effectively inhibit the formation of agglomerate particles on the positive electrode surface and improve the electrode quality and battery performance. Summary of the Invention

[0006] The purpose of the present invention is to provide a preparation method for inhibiting the formation of agglomerated particles on the positive electrode surface in response to the deficiencies of the existing technology, which can effectively inhibit the formation of agglomerated particles on the positive electrode surface and improve the quality of the electrode and battery performance.

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

[0008] A preparation method for inhibiting the generation of agglomerated particles on the surface of a positive electrode comprises the following steps:

[0009] S1. Raw material pretreatment: The positive electrode active material, conductive agent and binder are vacuum dried separately at a drying temperature of 60-90°C, a vacuum degree of -0.08-0.12 MPa, and a drying time of 2-4 hours;

[0010] S2. Slurry preparation: The pretreated material is placed in a stirring tank equipped with a pulsed vortex generator according to a preset ratio. The pulse frequency is 20-50 Hz, the amplitude is 2-5 mm, and the stirring time is 30-60 minutes. At the same time, the stirring temperature is controlled within the range of 15-25°C by the temperature control system.

[0011] S3. Ultrasonic dispersion treatment: The prepared slurry is introduced into an ultrasonic dispersion device with an ultrasonic power density of 300-600 W / L, a treatment time of 10-30 minutes, and a frequency of 40-60 kHz;

[0012] S4, slurry filtration: the treated slurry is sequentially passed through filtration devices with filtration precisions of 5μm, 2μm and 1μm, and the filtration pressure is 0.2~0.5MPa;

[0013] S5. Control before coating: Stir the filtered slurry evenly under the protection of inert gas and process it through a shear device with a shear rate of 800~1200s -1 , the processing time is 5~15 minutes.

[0014] Preferably, the material to be dried in S1 is subjected to magnetic separation purification treatment in advance, with a magnetic field strength of 0.5-1.5 T and 2-4 treatment times to remove ferromagnetic impurities in the material.

[0015] Preferably, the inner wall of the stirring tank in S2 is made of ceramic material and is provided with a magnetic metal ion capture device with a capture efficiency of ≥99.5%.

[0016] Preferably, the S2 slurry preparation process is carried out in a dry gas environment, the relative humidity of the environment is controlled at 5-15%, and the oxygen content is ≤100 ppm.

[0017] Preferably, the pulsed vortex generator in S2 is in a bidirectional alternating pulse mode, the time ratio of the forward pulse to the reverse pulse is 3:1, and the period of a single pulse is 2 to 5 seconds.

[0018] Preferably, the ultrasonic dispersion device in S3 adopts gradient ultrasonic technology, with an initial ultrasonic power of 50% of the rated power, which is increased by 10% every 5 minutes until it reaches full power.

[0019] Preferably, the filtering device in S4 includes a main filter and a bypass filter. The filtering accuracy of the bypass filter is one level higher than that of the main filter, and the bypass ratio is 20~30%. At the same time, an online particle monitoring device is set at the outlet of the filtering device. When the particle size is detected to be greater than 2μm, it automatically switches to full bypass filtration mode.

[0020] Preferably, the S5 medium shear device adopts a programmable shear mode, including a low shear pre-adaptation stage, a medium shear transition stage and a high shear intensification stage; wherein the shear rate in the low shear pre-adaptation stage is 300~500s -1 , the time is 2 minutes, and the shear rate in the medium shear transition stage is 500~800s -1 The time is 3 minutes, and the shear rate of the high shear strengthening stage is 800~1200s -1 , the time is 5 to 10 minutes.

[0021] Preferably, before the S3 ultrasonic dispersion treatment, 0.1-0.5 wt% of a surfactant is added to the slurry, wherein the surfactant is one or a mixture of polyvinyl pyrrolidone, polyethylene glycol and polyoxyethylene ether; the added amount is calculated based on the total mass of the slurry.

[0022] Preferably, it also includes S6, slurry online monitoring and correction: during the coating process, an online slurry agglomerate detection system is set up, and laser scattering detection technology is used. When it is detected that the agglomerate size is greater than 3μm or the number density exceeds 10 / cm², the slurry bypass ultrasonic redispersion device is automatically started, the ultrasonic power is 400~600W, the processing time is 30~60 seconds, and the main line slurry flow rate is adjusted at the same time, reducing it by 10~20% until the detection indicators return to normal.

[0023] In addition, the present invention also provides a positive electrode, which is prepared by the preparation method for inhibiting the generation of agglomerated particles on the positive electrode surface as described in any of the above paragraphs.

[0024] Compared with the prior art, the present invention has at least the following beneficial effects:

[0025] 1) This method pre-treats the raw materials through vacuum drying, eliminating moisture from the material at the source and preventing localized colloidization and agglomeration caused by moisture. At temperatures between 60°C and 90°C, the evaporation rate is optimal, effectively removing moisture from the material without degrading its performance. A vacuum of -0.08 to -0.12 MPa significantly lowers the boiling point of water and accelerates evaporation, while a treatment time of 2 to 4 hours ensures the complete removal of moisture from the material, fundamentally eliminating the impact of ambient humidity on agglomerate formation.

[0026] 2) The pulsed eddy current generator used in this invention creates a strong eddy current shear field in the slurry through a pulse frequency of 20-50 Hz and an amplitude of 2-5 mm. This effectively breaks down the weak interaction forces between the materials and prevents the initial agglomeration of the conductive agent and binder. Simultaneously, precise temperature control of 15-25°C maintains the appropriate viscosity of the slurry, preventing both rapid solvent volatilization and increased slurry viscosity caused by excessively high temperatures, and reducing dispersion efficiency caused by excessively low temperatures.

[0027] 3) The ultrasonic dispersion step introduced in this invention utilizes an ultrasonic power density of 300-600 W / L and a frequency of 40-60 kHz. The high energy and high temperature released when microbubbles collapse due to acoustic cavitation effectively break down existing small aggregates and prevent the formation of new ones. Ultrasonic treatment for 10-30 minutes ensures sufficient dispersion without damaging the material structure.

[0028] 4) This invention introduces a multi-stage filtration device, which can effectively intercept large particles and agglomerates in the slurry through step-by-step filtration at 5μm, 2μm, and 1μm, ensuring the uniformity of the coating slurry. The filtration pressure of 0.2-0.5MPa ensures sufficient filtration efficiency without causing deformation or damage to the filter material.

[0029] 5) The present invention introduces a shearing device, which takes 800~1200s -1 The high shear rate creates a uniform and stable nanoscale shear field in the slurry, which can continuously destroy the formation of small agglomerates and maintain a highly dispersed state of each component in the slurry. The inert gas protection effectively avoids the effects of oxygen and moisture on the slurry, further inhibiting the formation of agglomerates.

[0030] In summary, the present invention constructs a systematic agglomerate inhibition scheme through the synergistic effect of multiple processes such as raw material pretreatment, pulsed eddy current stirring, ultrasonic dispersion, multi-stage precision filtration and nano-shear flow field regulation, which can effectively solve the problem of agglomerate particles on the surface of the positive electrode and improve the performance and safety of lithium-ion batteries. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 1 is an SEM image of the positive electrode surface of Comparative Example 1, wherein a and b are SEM images of 300 μm and 10 μm, respectively;

[0032] Figure 2 1 is an SEM image of the positive electrode surface of Example 1, wherein c and d are SEM images of 300 μm and 10 μm, respectively. 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 preparation method for inhibiting the generation of agglomerated particles on the surface of a positive electrode, comprising the following steps:

[0035] S1. Raw material pretreatment: The positive electrode active material, conductive agent and binder are vacuum dried separately at a drying temperature of 60-90°C, a vacuum degree of -0.08-0.12 MPa, and a drying time of 2-4 hours;

[0036] S2. Slurry preparation: The pretreated material is placed in a stirring tank equipped with a pulsed vortex generator according to a preset ratio. The pulse frequency is 20-50 Hz, the amplitude is 2-5 mm, and the stirring time is 30-60 minutes. At the same time, the stirring temperature is controlled within the range of 15-25°C by the temperature control system.

[0037] S3. Ultrasonic dispersion treatment: The prepared slurry is introduced into an ultrasonic dispersion device with an ultrasonic power density of 300-600 W / L, a treatment time of 10-30 minutes, and a frequency of 40-60 kHz;

[0038] S4, slurry filtration: the treated slurry is sequentially passed through filtration devices with filtration precisions of 5μm, 2μm and 1μm, and the filtration pressure is 0.2~0.5MPa;

[0039] S5. Control before coating: Stir the filtered slurry evenly under the protection of inert gas and process it through a shear device with a shear rate of 800~1200s -1 , the processing time is 5~15 minutes.

[0040] Preferably, the material dried in S1 is pre-processed with a magnetic separation purification process with a magnetic field strength of 0.5 to 1.5 T and 2 to 4 treatments to remove ferromagnetic impurities in the material. The magnetic separation device used in the magnetic separation purification process generates a magnetic field by a permanent magnet or an electromagnet, is equipped with an automatic feeding system and a multi-stage magnetic field gradient separation unit, and the material moves in the magnetic field via a conveyor belt. The ferromagnetic impurities are adsorbed by the magnetic field on the magnetic poles, and the pure material falls into a collection container by gravity. The device is equipped with an automatic cleaning system. When a certain amount of impurities accumulate on the magnetic poles, the conveyor belt is suspended, the magnetic field is temporarily closed, and the automatic cleaning mechanism removes the adsorbed impurities to the waste collection area. The entire process is carried out in a closed environment to prevent secondary contamination, and high purity requirements are achieved through multiple treatments. Through magnetic separation purification, ferromagnetic impurities in the raw materials can be effectively removed. These impurities are often the core points of agglomerate formation. By removing them in advance, the probability of agglomerate formation can be reduced from the source.

[0041] In one embodiment of the present application, the inner wall of the stirring tank in S2 is made of ceramic material and is equipped with a magnetic metal ion capture device with a capture efficiency of ≥99.5%. The magnetic metal ion capture device mainly consists of three parts: first, a high-efficiency chelating agent system, which contains a variety of specific chelating agents for metal ions such as Fe, Ni, Co, and Mn, which are fixed on a micron-sized polymer carrier; second, a magnetic separation unit, which is an adsorption rod array made of rare earth permanent magnetic material, inserted into the slurry and rotatable, and coated with an anti-corrosion material on the surface; third, an automatic regeneration system, which consists of a cleaning device, a waste liquid collection and an adsorption rod surface treatment unit. During operation, the chelating agent forms a stable complex with the metal ions in the solution, and the magnetic separation unit rotates through the slurry, adsorbing the magnetic chelating agent-metal ion complex, and then moves out of the slurry area to enter the automatic regeneration system for cleaning and reprocessing, achieving continuous operation. This device can capture trace metal ions generated in the slurry in real time, prevent the metal ions from accumulating in the slurry and forming agglomeration centers, thereby inhibiting the formation of agglomerates. The ceramic inner wall design avoids the metal ion contamination problem that may be caused by metal mixing tanks, which is crucial to maintaining the high purity of the slurry.

[0042] In one embodiment of the present application, the S2 slurry preparation process is carried out in a dry gas environment, the relative humidity of the environment is controlled at 5~15%, and the oxygen content is ≤100ppm. In order to achieve this environmental condition, the stirring system needs to be set in a closed dry gas environment chamber, which is made of a stainless steel lining structure and is equipped with a multi-point sealing design and a micro-positive pressure protection system. The cabin is equipped with a high-precision humidity control system, including a condensing dehumidifier and a molecular sieve adsorption unit, which can continuously control the ambient humidity within the range of 5~15%; the oxygen content is controlled by nitrogen or argon replacement technology, equipped with a high-precision oxygen content analyzer, and the oxygen content in the cabin is monitored in real time to ensure that it does not exceed 100ppm. The environmental chamber is equipped with a glove operation port, a transfer window and an automatic material conveying system to facilitate operators to operate while keeping the environment sealed. A low humidity environment can effectively prevent localized colloidation and agglomeration caused by the reaction of hygroscopically sensitive materials in the slurry (such as NMP solvent and PVDF binder) with moisture. A low oxygen environment can prevent oxidation reactions on the surface of certain cathode materials (such as lithium-rich manganese-based materials), reducing the tendency to agglomerate due to changes in surface activity. A strictly controlled dry atmosphere is crucial for preventing environmental factors from affecting slurry uniformity and is also a key environmental condition for inhibiting the formation of agglomerates.

[0043] In one embodiment of the present application, the pulsed vortex generator in S2 adopts a bidirectional alternating pulse mode, with a forward pulse to reverse pulse time ratio of 3:1 and a single pulse period of 2 to 5 seconds. The pulsed vortex generator mainly consists of a control unit, a drive motor, a transmission system, and a stirring paddle. The control unit adopts a PLC control system, and the pulse frequency, amplitude, forward and reverse pulse time ratio, and pulse period can be set through the touch screen interface; the drive motor is a high-precision servo motor that can achieve fast forward and reverse switching; the transmission system includes a reducer and a balancing device to ensure stable torque transmission; the stirring paddle adopts a multi-dimensional fluid mechanics design, including a main paddle and an auxiliary paddle, which can generate directional shear force during both forward and reverse rotation. In the bidirectional alternating pulse mode, the forward pulse generates a downward vortex, which brings the upper layer of slurry into the lower layer; the reverse pulse generates an upward vortex, which brings the lower layer of slurry back to the upper layer, forming a three-dimensional circulating flow field. This positive and negative alternating pulse stirring mode can create a complex flow field structure, significantly enhancing the dispersion effect of particles in the slurry, while avoiding dead corners and material throwing phenomena that may be caused by unidirectional stirring, effectively preventing the formation of agglomerates. The 3:1 time ratio of the forward pulse to the reverse pulse and the 2-5 second pulse period are optimized parameters. They can keep the slurry fully mixed while giving the system enough relaxation time to reduce the damage to the material caused by shear stress.

[0044] In one embodiment of the present application, the ultrasonic dispersion device in S3 adopts gradient ultrasonic technology, with the initial ultrasonic power being 50% of the rated power, increasing by 10% every 5 minutes until reaching full power. The ultrasonic dispersion device consists of an ultrasonic generator, a horn, a multi-frequency ultrasonic transducer, a circulation pump, a temperature control system, and a real-time monitoring system. The ultrasonic generator can generate a stable high-frequency electrical signal, and the power can be continuously adjusted within the range of 0-600W / L; the horn is made of titanium alloy material, which has good acoustic properties and corrosion resistance; the multi-frequency ultrasonic transducer can simultaneously or alternately output ultrasonic waves of different frequencies in the range of 40-60kHz; the circulation pump ensures the uniform flow of the slurry during the ultrasonic treatment process; the temperature control system maintains the slurry temperature stable through jacket water circulation; the real-time monitoring system includes power monitoring, temperature monitoring, and spectrum analysis units, which can automatically adjust the ultrasonic parameters according to the slurry state. The gradient ultrasonic technology is the core feature of this system. By gradually increasing the ultrasonic power, the slurry gradually adapts to the ultrasonic environment, avoiding the material damage and local overheating problems that may be caused by direct full-power ultrasound. The main function of the initial 50% power stage is to pre-disperse large particle agglomerates. As the power increases by 10% every 5 minutes, smaller and more stable agglomerates can be gradually decomposed. Finally, when full power is reached, the decomposition of the finest agglomerates is completed, achieving effective dispersion in the entire particle size range, while significantly reducing the damage that the ultrasonic cavitation effect may cause to the active material.

[0045] In one embodiment of the present application, the filtration device in S4 includes a main filter and a bypass filter. The bypass filter has a higher filtration accuracy than the main filter, with a bypass ratio of 20-30%. An online particle monitoring device is installed at the outlet of the filtration device. When a particle size greater than 2 μm is detected, the device automatically switches to full bypass filtration mode. The filtration device consists of a feed unit, a main filtration unit, a bypass filtration unit, an online particle monitoring device, and a control system. The feed unit includes a constant pressure pump and pulsation suppressor to ensure stable feed pressure. The main filter unit consists of three stages of precision filters connected in series, with filtration accuracies of 5μm, 2μm, and 1μm, respectively. Each stage of the filter adopts a foldable, large-area design and is equipped with an automatic backwash function. The bypass filter unit is installed in parallel with the main filter unit, with filtration accuracies of 4μm, 1.5μm, and 0.8μm, respectively, one level higher than the main filter. The online particle monitoring device uses the laser scattering principle and consists of a light source, optical system, detector, and data processing unit. It can detect the size and number of particles in the slurry flowing through the system in real time. The control system automatically adjusts the flow ratio between the main filter and the bypass based on the online monitoring results. When a particle size greater than 2μm is detected, the system automatically switches to full bypass filtration mode. The design of the main and bypass filters greatly improves the fault tolerance of the filtration device. If the main filter is damaged or the filtration efficiency decreases, the bypass filter can be replenished in time to ensure filtration quality. A bypass ratio of 20-30% is an optimized parameter that ensures sufficient processing capacity without excessively increasing system complexity and cost. The online particle monitoring device and automatic control function make the entire filtration system intelligent and adaptive, enabling timely response to emergencies and further ensuring high-quality slurry filtration.

[0046] In one embodiment of the present application, the shearing device in S5 adopts a programmable shearing mode, including a low shear pre-adaptation stage (300-500s -1 , 2 minutes), medium shear transition stage (500~800s -1 , 3 minutes) and high shear strengthening stage (800~1200s -1, 5~10 minutes). The shearing device consists of a high-precision shear generator, a microchannel flow unit, a pressure control system, a real-time shear rate monitoring device and a programming control unit. The high-precision shear generator adopts a rotor-stator structure, and the rotor is driven by a high-precision servo motor. The rotation speed can be precisely controlled within the range of 0-10000rpm; the microchannel flow unit is composed of multiple parallel microchannels, and an array of micro-obstacles is provided in the channel, which can generate a complex microscale flow field; the pressure control system maintains the stable flow of the slurry in the system; the real-time shear rate monitoring device calculates the real-time shear rate of the slurry at different positions through a micro-pressure sensor array and a flow rate sensor; the programming control unit can automatically adjust the system parameters according to the preset program to realize a programmable shear mode. This step-by-step shear rate increase processing mode is designed based on the principles of material science and rheology. The low shear pre-adaptation stage (300~500s -1 , 2 minutes) is mainly to allow the slurry to adapt to the shear environment and avoid structural damage caused by sudden high shear; the medium shear transition stage (500~800s -1 , 3 minutes) to further improve the dispersion effect and prepare for high shear; high shear strengthening stage (800~1200s -1 , 5-10 minutes) can completely break down any remaining microaggregates and prevent the formation of new aggregates through continuous high shear force. This progressive shearing method maximizes the destruction of aggregates while protecting the integrity of the active material, providing an optimized treatment solution that balances dispersion and material protection.

[0047] In one embodiment of the present application, before the S3 ultrasonic dispersion treatment, 0.1~0.5wt% of a surfactant is added to the slurry, and the surfactant is a mixture of one or more of polyvinyl pyrrolidone, polyethylene glycol and polyoxyethylene ether; the added amount is calculated based on the total mass of the slurry. The addition of surfactants plays an important role in enhancing the ultrasonic dispersion effect. These high-molecular surfactants can be adsorbed on the surface of the particles, forming a steric hindrance effect, preventing the particles from re-aggregating. Polyvinyl pyrrolidone has excellent solubility and stability and is suitable for a variety of solvent systems; polyethylene glycol has good biocompatibility and low toxicity; and polyoxyethylene ether has strong emulsification and dispersion capabilities. These surfactants, within the addition amount range of 0.1~0.5wt%, can effectively exert a dispersing effect without excessively increasing the slurry viscosity or affecting the electrochemical performance. After adding the surfactant, the protective layer formed on the surface of the particles can effectively prevent the particles from re-aggregating after ultrasonic treatment, significantly improving the lasting effect of ultrasonic dispersion.

[0048] In one embodiment of the present application, S6, online slurry monitoring and correction, is further included: During the coating process, an online slurry agglomerate detection system is set up, using laser scattering detection technology. When the agglomerate size is detected to be greater than 3 μm or the number density exceeds 10 / cm², the slurry bypass ultrasonic redispersion device is automatically activated with an ultrasonic power of 400-600W and a processing time of 30-60 seconds. At the same time, the main line slurry flow rate is adjusted to reduce by 10-20% until the detection indicators return to normal. The slurry online monitoring and correction system consists of an online detection unit, a data analysis unit, a bypass ultrasonic redispersion unit, and a control system. The online detection unit utilizes laser scattering technology, including a semiconductor laser light source (650nm), an optical path system, a scattered light collector, and a high-sensitivity photodetector array. This enables real-time detection of aggregate size distribution and number density in the flowing slurry. The data analysis unit employs a high-speed data processing algorithm to analyze the scattered signals and calculate aggregate parameters in real time. The bypass ultrasonic redispersion unit, comprised of a high-power ultrasonic transducer (400-600W), a flow cell, and a cooling system, enables rapid and efficient redispersion of the diverted slurry. The control system automatically adjusts the mainline to bypass flow ratio based on the detection results, controlling the ultrasonic power and processing time. A unique feature of this system is its closed-loop control of slurry quality, enabling not only problem identification but also automated corrective action. When aggregates larger than 3μm in size or exceeding a critical number density of 10 / cm² are detected, the system automatically initiates an emergency response process, diverting some of the slurry to the bypass ultrasonic redispersion unit for intensive treatment while also appropriately reducing the mainline slurry flow rate to allow the system sufficient response time. This real-time monitoring and correction mechanism can effectively deal with possible fluctuations in slurry quality during the coating process, ensuring that the surface quality of the final coated electrode is stable and consistent.

[0049] According to the second aspect of the present application, the present application also provides a positive electrode, including a current collector and a positive electrode active slurry layer coated on the current collector, which is prepared by the preparation method for inhibiting the generation of agglomerate particles on the positive electrode surface as described in any of the above paragraphs.

[0050] The equipment and system used in the present invention can be purchased commercially, and their structures are briefly described as follows:

[0051] 1. Magnetic separation purification device

[0052] The magnetic separation purification device used in the present invention is mainly composed of the following parts:

[0053] (1) Magnetic field generating system: uses rare earth permanent magnet materials or electromagnets to generate a strong magnetic field of 0.5~1.5T, with adjustable magnetic field strength and equipped with a precision magnetic field measurement feedback system;

[0054] (2) Material conveying system: including a vibrating feeder, an anti-static conveyor belt and an angle-adjustable bracket to ensure that the material is evenly distributed in the magnetic field;

[0055] (3) Magnetic field gradient separation unit: It uses a gradient magnetic field composed of multiple magnetic poles with magnetic field strength arranged from weak to strong to achieve graded capture of impurities with different magnetic susceptibilities;

[0056] (4) Automatic cleaning system: equipped with a reversible conveyor belt and a compressed air purge device. When a certain amount of impurities accumulate on the magnetic pole, the system automatically stops working, the conveyor belt runs in the reverse direction, and the compressed air purge device removes the adsorbed impurities.

[0057] (5) Sealed dust cover: The entire device is placed in a sealed dust cover to prevent external contamination and dust from escaping during the processing process;

[0058] (6) Control system: PLC control system is used to realize automatic control of material processing speed, magnetic field strength, cleaning cycle, and record processing data.

[0059] In actual operation, the material is evenly fed onto a conveyor belt via a vibrating feeder, forming a thin layer on the belt. It then passes through a gradient magnetic field, where ferromagnetic impurities are attracted to the magnetic poles. The pure material then falls by gravity into a collection container. This device operates continuously, repeating the process 2 to 4 times to effectively remove ferromagnetic impurities from the material, keeping the impurity content to an extremely low level.

[0060] 2. Pulsed vortex generator

[0061] Among them, the pulsed vortex generator is a highly efficient stirring device, and its main components include:

[0062] (1) Control unit: It uses a high-performance industrial computer and real-time control system with a touch screen human-machine interface, which can accurately set and control the pulse frequency (20~50Hz), amplitude (2~5mm), forward and reverse pulse time ratio and pulse period;

[0063] (2) Drive system: It uses a high-precision servo motor with high response speed and torque control capability, capable of fast forward and reverse switching and precise amplitude control;

[0064] (3) Transmission system: including reducer, torque limiter and balancing system, ensuring stable and efficient pulse transmission while avoiding overload damage;

[0065] (4) Agitator system: It adopts a multi-layer and multi-dimensional design, including a main agitator and an auxiliary agitator. The main agitator is responsible for generating the main vortex field, while the auxiliary agitator is responsible for destroying the dead zone and enhancing the mixing effect. The two work together to form a three-dimensional vortex field.

[0066] (5) Sealing system: It adopts a combination of mechanical seal and magnetic seal design to ensure good sealing under high-frequency pulse conditions and prevent external contamination and internal leakage;

[0067] (6) Monitoring system: equipped with torque sensor, vibration sensor and temperature sensor to monitor the equipment operation status in real time and automatically adjust or alarm if any abnormality occurs.

[0068] When the pulsed vortex generator is operating, the drive system, according to the control unit's instructions, moves the agitator at a set frequency, amplitude, and pattern, generating a complex vortex field in the slurry. In bidirectional alternating pulse mode, the forward pulse to reverse pulse time ratio is 3:1, and a single pulse period is 2 to 5 seconds. This unique stirring mode creates a powerful and multi-dimensional shear force that effectively breaks down the micro-agglomeration structure in the slurry while maintaining good macro-mixing effects.

[0069] 3. Ultrasonic dispersion device

[0070] Among them, the ultrasonic dispersion device is a high-efficiency dispersion device, and its main components include:

[0071] (1) Ultrasonic generator: It uses digital control technology to generate stable high-frequency electrical signals. The output power can be continuously adjusted within the range of 0-600W / L and has overload protection and power feedback control functions.

[0072] (2) Multi-frequency ultrasonic transducer: Made of piezoelectric ceramic material, it can simultaneously or alternately output ultrasonic waves of different frequencies in the range of 40-60kHz. The multi-frequency superposition technology enhances the uniformity of the cavitation effect;

[0073] (3) Amplitude transformer: Made of titanium alloy, it has excellent acoustic performance and corrosion resistance, and can efficiently transmit ultrasonic energy;

[0074] (4) Flow processing unit: including flow trough, guide plate and dispersion enhancement structure, to ensure the uniform flow of slurry in the ultrasonic field and avoid dead zones;

[0075] (5) Circulation pump system: It adopts magnetic drive pump with no shaft seal design to avoid pollution and provide stable slurry circulation flow;

[0076] (6) Temperature control system: A double-layer jacket design is used to control the slurry temperature through a precise temperature-controlled water circulation system to prevent overheating during ultrasonic treatment;

[0077] (7) Real-time monitoring system: including power monitoring, temperature monitoring, spectrum analysis and acoustic cavitation monitoring units, which can evaluate the ultrasonic effect in real time and automatically adjust the parameters.

[0078] The unique feature of this device is its gradient ultrasound technology. The device is programmed to start at 50% of the rated power, increasing by 10% every five minutes until it reaches full power. This gradual increase in power first breaks down large aggregates, then gradually decomposes smaller, more stable aggregate structures. This avoids the local overheating and material damage that can result from direct high-power treatment, achieving a more uniform and effective dispersion effect.

[0079] 4. Filtration device

[0080] The filtering device used in the present invention is a high-precision, high-reliability slurry filtering device, the main components of which include:

[0081] (1) Feeding unit: including constant pressure pump, pulsation suppressor and pressure sensor to ensure stable feeding pressure (0.2~0.5MPa);

[0082] (2) Main filter unit: It consists of three stages of precision filter mesh connected in series, with filtration accuracy of 5μm, 2μm and 1μm respectively. Each stage of filter mesh adopts a folded large-area design and is made of modified PTFE or polysulfone, which has high strength and solvent resistance;

[0083] (3) Bypass filter unit: It is set in parallel with the main filter unit and contains three levels of filter screens with filtration precisions of 4μm, 1.5μm and 0.8μm, which is one level higher than the main filter screen;

[0084] (4) Flow distribution system: It consists of a precision flow control valve and an electric control valve, which can adjust the flow ratio of the main filter and the bypass according to the control instructions (the bypass ratio is 20~30%);

[0085] (5) Online particle monitoring device: Using the laser scattering principle, it includes a semiconductor laser light source (650nm), an optical path system, a scattered light collector, and a high-sensitivity photodetector array, which can detect the size distribution of particles in the slurry in real time;

[0086] (6) Automatic backwash unit: including backwash pump, flushing liquid storage tank and program control system, which can automatically backwash when the filter resistance increases, thereby extending the service life of the filter;

[0087] (7) Control system: Using industrial computers and software, automatically adjust the filtering parameters and flow distribution according to the online monitoring results and system status.

[0088] The unique feature of this device is its parallel design of the main and bypass filters, as well as its online particle monitoring and automatic control capabilities. When the online monitoring device detects particles larger than 2μm, the system automatically directs all slurry into the bypass filtration unit, where it is processed through a higher-precision filter to ensure the quality of the output slurry. This design significantly improves the reliability and adaptability of the filtration unit, enabling it to cope with a variety of possible filter failures and slurry anomalies.

[0089] 5. Shearing device

[0090] The shearing device used in the present invention is a high-precision device for final slurry control, and its main components include:

[0091] (1) High-precision shear generator: It adopts a rotor-stator structure, and the rotor is driven by a high-precision servo motor with a speed range of 0-10000rpm and a speed stability of ±0.1%, which can generate a precisely controllable shear field;

[0092] (2) Microchannel flow unit: It consists of multiple parallel microchannels with a channel width of 50-200 μm and an array of micro-obstacles inside, which can generate complex microscale flow fields and enhance the shear effect;

[0093] (3) Pressure control system: including precision pressure regulator, pressure sensor and feedback control unit to maintain stable flow of slurry in the system;

[0094] (4) Inert gas protection system: including gas purification unit, flow controller and sealing cover, providing inert gas (nitrogen or argon) protection environment to prevent the influence of oxygen and moisture;

[0095] (5) Real-time shear rate monitoring device: through the micro pressure sensor array and flow rate sensor, combined with the computational fluid dynamics model, the real-time shear rate of the slurry at different positions is calculated;

[0096] (6) Programming control unit: Based on industrial computers and dedicated software, it can realize preset programmable shear modes, including low shear pre-adaptation stage (300~500s -1 , 2 minutes), medium shear transition stage (500~800s -1 , 3 minutes) and high shear strengthening stage (800~1200s -1 , 5-10 minutes);

[0097] (7) Temperature control system: Use a precision temperature control device to keep the processing temperature within the set range (usually 15~25℃) to avoid shear heat affecting the slurry properties.

[0098] The device's key features lie in its programmable shear mode and microchannel flow cell design. The programmable shear mode optimizes the shearing process based on slurry characteristics and processing requirements. The microchannel flow cell, through its structural design, creates a microscopic shear field within the macroscopic flow, significantly enhancing the shearing effect while reducing dead zones and uneven areas. This nanoscale shearing process effectively breaks down and prevents the formation of microaggregates, achieving optimal slurry dispersion.

[0099] 6. Slurry online monitoring and correction system

[0100] The slurry online monitoring and correction system of the present invention is a real-time quality control device, the main components of which include:

[0101] (1) Online detection unit: Using laser scattering technology, including a semiconductor laser light source (650nm), an optical path system, a scattered light collector, and a high-sensitivity photodetector array, it can detect the size distribution and number density of aggregates in the flowing slurry in real time;

[0102] (2) Data analysis unit: Using a high-speed data processing system and dedicated algorithms, it analyzes the scattering signal in real time, calculates the aggregate parameters, and compares them with the preset thresholds;

[0103] (3) Bypass ultrasonic redispersion unit: including high-power ultrasonic transducer (400-600W), focuser, flow cell and cooling system, which can quickly and efficiently redisperse the diverted slurry;

[0104] (4) Flow control system: It consists of a precision flow control valve and a fast-response electric valve, which can quickly adjust the diversion ratio between the main line and the bypass;

[0105] (5) Control system: Using real-time control computers and dedicated software, the start and stop of the bypass ultrasonic redispersion unit and parameter adjustment are automatically controlled according to the test results, while the main line slurry flow rate is controlled at the same time.

[0106] When the system is working, the slurry is first detected by the online detection unit for agglomerate detection, and the data analysis unit processes the detection signal in real time and calculates the agglomerate parameters. When it is detected that the agglomerate size is greater than 3μm or the number density exceeds 10 / cm², the control system automatically starts the emergency treatment process: on the one hand, part of the slurry (usually 20~30%) is diverted to the bypass ultrasonic redispersion unit for enhanced treatment, with a processing power of 400~600W and a time of 30~60 seconds; on the other hand, the main line slurry flow rate is appropriately reduced (reduced by 10~20%) to extend the system response time. The redispersed slurry is re-entered into the main line, mixed with the untreated slurry, and then continues to enter the coating system. The whole process continues until the detection indicators return to normal.

[0107] This closed-loop control mechanism can monitor the slurry quality in real time and take corrective measures immediately when problems are found, ensuring the continuity of the coating process and the stability of the electrode quality.

[0108] The implementation and advantages of this application will be further explained below with reference to specific embodiments.

[0109] Example 1

[0110] This embodiment provides a preparation method for suppressing the generation of agglomerated particles on the surface of a positive electrode, comprising the following steps:

[0111] S1: Raw material pretreatment: NCM811 positive electrode active material, conductive carbon black and PVDF binder were vacuum dried at 75°C, vacuum degree of -0.1 MPa and drying time of 3 hours.

[0112] S2: Slurry preparation: The pretreated materials were placed in a stirring tank equipped with a pulsed vortex generator at a mass ratio of 92:4:4. The pulse frequency was 35 Hz, the amplitude was 3.5 mm, and the stirring time was 45 minutes. The stirring temperature was controlled at 20°C by a temperature control system. The stirring tank had a ceramic inner wall and was equipped with a magnetic metal ion capture device. During the entire stirring process, the relative humidity of the environment was controlled at 10%, and the oxygen content was ≤50 ppm.

[0113] S3: Ultrasonic dispersion treatment: 0.3 wt% of polyvinyl pyrrolidone surfactant was added to the slurry, and then the prepared slurry was introduced into an ultrasonic dispersion device. Gradient ultrasound technology was used with an initial ultrasonic power of 225 W / L (50% of the rated power) and increased by 10% every 5 minutes until it reached 450 W / L. The total treatment time was 20 minutes and the frequency was 50 kHz.

[0114] S4: Slurry filtration: The treated slurry is sequentially passed through filtration devices with filtration precisions of 5μm, 2μm, and 1μm, with a filtration pressure of 0.3MPa; the filtration device includes a main filter and a bypass filter, with a bypass ratio of 25%. An online particle monitoring device is installed at the outlet of the filtration device;

[0115] S5: Before coating, the filtered slurry was stirred evenly under argon protection and processed through a shear device. The programmable shear mode was used: low shear pre-adaptation stage (400s -1 , 2 minutes), medium shear transition stage (650s -1 , 3 minutes) and high shear strengthening stage (1000s -1 , 8 minutes);

[0116] S6: Online monitoring and correction of slurry. During the coating process, an online detection system for slurry agglomerates is set up, and laser scattering detection technology is used to monitor the size and number of agglomerates in the slurry. When the agglomerate size is detected to be greater than 3μm or the number density exceeds 10 / cm², the slurry bypass ultrasonic redispersion device is automatically started with an ultrasonic power of 500W and a processing time of 45 seconds. At the same time, the main line slurry flow rate is adjusted to reduce it by 15% until the detection indicators return to normal.

[0117] Example 2

[0118] This embodiment provides a preparation method for suppressing the generation of agglomerated particles on the surface of a positive electrode, comprising the following steps:

[0119] S1: Raw material pretreatment: LFP cathode active material, conductive carbon black, and PVDF binder were subjected to magnetic separation purification treatment at a magnetic field strength of 1.0T for three times to remove ferromagnetic impurities in the materials; then vacuum drying was performed at a drying temperature of 80°C, a vacuum degree of -0.09MPa, and a drying time of 2.5 hours;

[0120] S2: Slurry preparation: The pretreated material was placed in a stirring tank equipped with a pulsed vortex generator at a mass ratio of 90:5:5. A bidirectional alternating pulse mode was used, with a forward pulse to reverse pulse time ratio of 3:1, a single pulse period of 3 seconds, a pulse frequency of 30 Hz, an amplitude of 4 mm, and a stirring time of 40 minutes. The stirring temperature was controlled at 18°C ​​by a temperature control system. During the entire stirring process, the relative humidity of the environment was controlled at 8%, and the oxygen content was ≤80 ppm.

[0121] S3: Ultrasonic dispersion treatment: 0.2 wt% of polyethylene glycol and 0.2 wt% of polyoxyethylene ether mixed surfactant were added to the slurry, and then the prepared slurry was introduced into an ultrasonic dispersion device. Gradient ultrasound technology was used with an initial ultrasonic power of 200 W / L (50% of the rated power), which was increased by 10% every 5 minutes until it reached 400 W / L. The total treatment time was 25 minutes, and the frequency was 45 kHz.

[0122] S4: Slurry filtration: The treated slurry is sequentially passed through filtration devices with filtration precisions of 5μm, 2μm, and 1μm, with a filtration pressure of 0.4MPa; the filtration device includes a main filter and a bypass filter, with a bypass ratio of 30%;

[0123] S5: Before coating, the filtered slurry is stirred evenly under nitrogen protection and processed through a shear device. The programmable shear mode is used: low shear pre-adaptation stage (450s -1 , 2 minutes), medium shear transition stage (700s -1 , 3 minutes) and high shear strengthening stage (1100s-1 , 10 minutes);

[0124] S6: Online monitoring and correction of slurry. During the coating process, an online detection system for slurry agglomerates is set up, and laser scattering detection technology is used to monitor the size and number of agglomerates in the slurry. When the agglomerate size is detected to be greater than 3μm or the number density exceeds 8 / cm², the slurry bypass ultrasonic redispersion device is automatically started with an ultrasonic power of 550W and a processing time of 40 seconds. At the same time, the main line slurry flow rate is adjusted to reduce it by 12% until the detection indicators return to normal.

[0125] Example 3

[0126] This embodiment provides a preparation method for suppressing the generation of agglomerated particles on the surface of a positive electrode, comprising the following steps:

[0127] S1: Raw material pretreatment: NCA positive electrode active material, conductive carbon black and PVDF binder were subjected to magnetic separation purification treatment with a magnetic field strength of 1.5T and a treatment frequency of 4 times; then vacuum drying was performed with a drying temperature of 85°C, a vacuum degree of -0.11MPa, and a drying time of 3.5 hours;

[0128] S2: Slurry preparation: The pretreated materials were placed in a stirring tank equipped with a pulsed vortex generator at a mass ratio of 93:3:4. The pulse frequency was 40 Hz, the amplitude was 4.5 mm, and the stirring time was 50 minutes. The stirring temperature was controlled at 22°C by a temperature control system. The stirring tank had a ceramic inner wall and was equipped with a magnetic metal ion capture device with a capture efficiency of 99.8%. During the entire stirring process, the relative humidity of the environment was controlled at 6%, and the oxygen content was ≤30 ppm.

[0129] S3: Ultrasonic dispersion treatment: 0.4 wt% of polyvinyl pyrrolidone surfactant was added to the slurry, and then the prepared slurry was introduced into an ultrasonic dispersion device. Gradient ultrasound technology was used with an initial ultrasonic power of 250 W / L (50% of the rated power) and increased by 10% every 5 minutes until it reached 500 W / L. The total treatment time was 15 minutes and the frequency was 55 kHz.

[0130] S4: Slurry filtration: The treated slurry is sequentially passed through filtration devices with filtration precisions of 5μm, 2μm, and 1μm, with a filtration pressure of 0.35MPa. The filtration device includes a main filter and a bypass filter, with a bypass ratio of 22%. An online particle monitoring device is installed at the outlet of the filtration device. When the particle size is detected to be greater than 2μm, it automatically switches to full bypass filtration mode.

[0131] S5: Before coating, the filtered slurry was stirred evenly under argon protection and processed through a shear device. The programmable shear mode was used: low shear pre-adaptation stage (500s-1 , 2 minutes), medium shear transition stage (800s -1 , 3 minutes) and high shear strengthening stage (1200s -1 , 7 minutes);

[0132] S6: Online monitoring and correction of slurry. During the coating process, an online detection system for slurry agglomerates is set up, and laser scattering detection technology is used to monitor the size and number of agglomerates in the slurry. When the agglomerate size is detected to be greater than 2.5μm or the number density exceeds 7 / cm², the slurry bypass ultrasonic redispersion device is automatically started with an ultrasonic power of 600W and a processing time of 35 seconds. At the same time, the main line slurry flow rate is adjusted to reduce by 18% until the detection indicators return to normal.

[0133] Comparative Example 1

[0134] This comparative example provides a conventional method for preparing a positive electrode slurry, comprising the following steps:

[0135] S1: conventional drying, the positive electrode active material (NCM811), conductive carbon black and PVDF binder were dried in an oven at 80 °C for 4 h;

[0136] S2: conventional stirring, the dried materials were added into a conventional stirring tank according to a mass ratio of 92:4:4, the stirring speed was 800 rpm, the stirring time was 3 hours, and the stirring temperature was room temperature (about 25°C);

[0137] S3: Conventional filtration, filtering the slurry through a 20 μm single-stage filter;

[0138] S4: Direct coating, the filtered slurry is directly coated without additional conditioning.

[0139] Comparative Example 2

[0140] This comparative example provides an improved method for preparing a positive electrode slurry, comprising the following steps:

[0141] S1: conventional drying, the positive electrode active material (LFP), conductive carbon black and PVDF binder were dried in an oven at 80 °C for 6 h;

[0142] S2: Improve the stirring. Put the dried materials into a high-speed disperser at a mass ratio of 90:5:5, with a stirring speed of 1200 rpm, a stirring time of 2 hours, and a stirring temperature of 20°C.

[0143] S3: ultrasonic treatment, the slurry is ultrasonically treated with an ultrasonic power of 200 W / L and a treatment time of 10 minutes;

[0144] S4: single-stage filtration, filtering the slurry through a 10 μm filter;

[0145] S5: Direct coating, the filtered slurry is directly coated without additional conditioning.

[0146] Comparative Example 3

[0147] This comparative example provides a method for preparing a positive electrode slurry including metal contamination control, comprising the following steps:

[0148] S1: Material magnetic separation: the positive electrode active material (NCA), conductive carbon black and PVDF binder were magnetically separated with a magnetic field strength of 0.5 T for one treatment; then dried in an 80°C oven for 5 hours;

[0149] S2: conventional stirring, the dried materials were added into a stainless steel stirring tank according to a mass ratio of 93:3:4, the stirring speed was 1000 rpm, the stirring time was 2.5 hours, and the stirring temperature was room temperature (about 25°C);

[0150] S3: Double-stage filtration, filtering the slurry through 15μm and 8μm filter screens in sequence;

[0151] S4: Direct coating, the filtered slurry is directly coated without additional conditioning.

[0152] The slurries prepared in the above examples and comparative examples were coated into positive electrode sheets and batteries, and the following performance tests were performed. The test results are shown in Tables 1 and 2.

[0153] 1. Agglomerate particle density test: Observe the electrode surface using an optical microscope at 400x magnification. Randomly select 10 areas (1 cm² each) and calculate the average number of agglomerate particles (size > 10 μm).

[0154] 2. Agglomerate size distribution test: Use a laser particle size analyzer to measure the size distribution of particles in the slurry and record the D90 value (indicating that 90% of the particles are smaller than this value).

[0155] 3. Pole surface roughness test: Use a surface roughness meter to measure the roughness (Ra value) of the pole surface, and measure each sample 10 times to take the average value.

[0156] 4. Positive electrode uniformity test: Using an X-ray fluorescence spectrometer (XRF), 25 measurement points were evenly selected within a 10 cm x 10 cm area to measure the elemental content of the active material and calculate the relative standard deviation (RSD). The uniformity score = (1-RSD) × 10, with a maximum score of 10.

[0157] 5. Battery initial charge and discharge efficiency test: Assemble the prepared positive electrode sheets into 2032-type button cells and perform the initial charge and discharge at a 0.1C rate. Calculate the initial charge and discharge efficiency.

[0158] 6. Battery cycle performance test: The assembled battery was cycled 300 times at a 1C rate and the capacity retention was measured.

[0159] 7. Battery safety test: Use the needle penetration test method to observe whether the battery catches fire or explodes, and record the maximum temperature rise.

[0160] Table 1 Pole performance test results

[0161] Test items Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 Comparative Example 3 Agglomerate particle density (pieces / cm²) 2.1 1.8 1.5 35.6 18.4 12.7 Aggregate size D90 (μm) 4.2 3.8 3.5 25.3 15.6 12.3 Pole surface roughness Ra (μm) 0.32 0.28 0.25 0.87 0.63 0.52 Positive electrode uniformity score (points) 9.5 9.6 9.8 7.2 8.1 8.5 Metal impurity content (ppm) <3 <2 <1 42 28 15

[0162] Table 2 Battery performance test results

[0163] Test items Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 Comparative Example 3 First charge and discharge efficiency (%) 89.5 90.3 91.2 83.1 85.2 86.5 300 cycle capacity retention rate (%) 88.3 89.5 90.6 75.6 79.8 82.1 Rate performance (5C / 0.5C) (%) 86.2 87.8 89.3 70.5 75.2 78.4 Puncture test temperature rise (℃) 42 38 35 132 85 64 Impedance growth rate (after 300 cycles) (%) 15.3 13.6 11.8 58.7 42.3 35.2

[0164] The above test results are analyzed as follows:

[0165] 1. Comparative Analysis between Examples and Comparative Examples:

[0166] (1) Agglomerate particle density: The agglomerate particle density of Examples 1-3 is significantly lower than that of Comparative Examples 1-3. The agglomerate particle density of Example 3 is the lowest, only 1.5 particles / cm², while the agglomerate particle density of Comparative Example 1 is as high as 35.6 particles / cm². This shows that the preparation method of the present invention can effectively inhibit the formation of agglomerate particles on the positive electrode surface. In addition, the comparison Figure 1 and Figure 2 It can be seen that the surface of the positive electrode of Example 1 of the present invention is smooth, and the positive electrode slurry of the present invention is fully dispersed and evenly distributed on the surface; while there are a large number of agglomerated particles on the surface of the positive electrode of Comparative Example 1, and the positive electrode slurry has agglomerates on the surface and is not fully dispersed.

[0167] (2) Aggregate Size: The agglomerate size D90 values ​​of Examples 1-3 were much smaller than those of Comparative Examples 1-3. The agglomerate size D90 value of Example 3 was only 3.5 μm, while the agglomerate size D90 value of Comparative Example 1 reached 25.3 μm. This demonstrates that the preparation method of the present invention can not only reduce the number of agglomerate particles, but also significantly reduce the size of the agglomerate particles.

[0168] (3) Pole piece surface roughness: The surface roughness Ra values ​​of the pole pieces of Examples 1-3 are significantly lower than those of Comparative Examples 1-3, indicating that the pole piece surfaces prepared by the present invention are smoother and more uniform, which is beneficial to improving the electrode / electrolyte contact area and electrochemical performance.

[0169] (4) Positive electrode sheet uniformity: The positive electrode sheet uniformity scores of Examples 1-3 are higher than those of Comparative Examples 1-3, indicating that the preparation method of the present invention can significantly improve the uniformity of the positive electrode sheet.

[0170] (5) Metal impurity content: The metal impurity content of Examples 1-3 was much lower than that of Comparative Examples 1-3. In particular, the metal impurity content of Example 3 was less than 1 ppm, while the metal impurity content of Comparative Example 1 was as high as 42 ppm. This demonstrates that the magnetic separation purification process and magnetic metal ion capture device of the present invention can effectively remove metal impurities from the material.

[0171] (6) Battery Performance: As can be seen from Table 2, the battery performance of Examples 1-3 is significantly superior to that of Comparative Examples 1-3, particularly in terms of initial charge and discharge efficiency, cycle life, rate capability, and safety. This fully demonstrates the significant impact of the suppression of agglomerate particles on battery performance.

[0172] 2. Comparative Analysis between Various Examples:

[0173] (1) Example 3 performed best in all indicators, which was mainly due to the use of higher intensity magnetic separation purification treatment (1.5T, 4 times), stricter environmental control (relative humidity 6%, oxygen content ≤30ppm), and more optimized ultrasonic dispersion and shear flow field control parameters.

[0174] (2) The NCA material system of Example 3 exhibits certain advantages in energy density and electrochemical performance compared to the NCM811 system of Example 1 and the LFP system of Example 2. More importantly, the preparation method of the present invention exhibits significant agglomeration suppression effects in various cathode material systems, demonstrating the versatility and adaptability of the method.

[0175] (3) The online monitoring and correction strategy adopted in Example 3 is more stringent (the redispersion system is activated when the aggregate size is >2.5 μm or the number density is >7 / cm²), which effectively avoids the problem of aggregate accumulation that may occur during the coating process.

[0176] 3. Analysis of technical effects of each process step:

[0177] (1) Raw material pretreatment: Magnetic separation and purification combined with vacuum drying pretreatment can remove ferromagnetic impurities and moisture from the material at the source, providing clean, dry raw materials for subsequent slurry preparation. Comparative Examples 1 and 2 only used conventional drying, while Comparative Example 3, although subjected to magnetic separation treatment, was insufficient in intensity and frequency, resulting in a high level of residual metal impurities.

[0178] (2) Slurry Preparation: Compared with conventional stirring and high-speed dispersion, the pulsed vortex generator can generate stronger shear force and more uniform mixing effect. In particular, the bidirectional alternating pulse mode (Example 2) and the high-frequency and high-amplitude setting (Example 3) perform better. At the same time, the ceramic inner wall stirring tank and the magnetic metal ion capture device effectively prevent metal contamination during the stirring process.

[0179] (3) Ultrasonic dispersion: Gradient ultrasound technology can more effectively break up aggregates than constant power ultrasound, while reducing damage to the material. The addition of surfactant further improves the dispersion effect. In particular, the addition of 0.4 wt% surfactant in Example 3 combined with 55 kHz high-frequency ultrasound shows the best dispersion effect.

[0180] (4) Multi-stage precision filtration: Three-stage precision filtration (5μm, 2μm, 1μm) significantly outperforms single-stage or double-stage filtration and can more effectively intercept aggregate particles. The design of the main filter and bypass filter, as well as the online particle monitoring device (Example 3), ensure the stability and reliability of the filtration effect.

[0181] (5) Nano-shear flow field control: Programmable shear mode (low-medium-high three stages) can better protect the material structure than direct high shear and achieve better dispersion effect. -1 The high shear rate combined with inert gas protection effectively prevents the reformation of agglomerates.

[0182] (6) Online Monitoring and Correction: This step ensures the continuous suppression of agglomerate particles throughout the coating process through real-time monitoring and automatic correction. Comparative Examples 1-3 all lack this critical step, resulting in the inability to prevent agglomeration during the coating process even with good pre-treatment.

[0183] In summary, the preparation method for inhibiting the generation of agglomerate particles on the surface of the positive electrode of the present invention has constructed a systematic, full-process agglomerate inhibition solution through the synergistic effect of multiple steps, from raw material pretreatment to slurry preparation, ultrasonic dispersion, precision filtration, pre-coating regulation and control, and online monitoring and correction. Compared with the single or partial measures in the comparative example, the present invention can solve the problem of agglomerate particles on the surface of the positive electrode more comprehensively and effectively. The test results show that the density of the agglomerate particles of the pole piece prepared by the present invention is reduced by 85%-95%, the size of the agglomerate is reduced by 75%-85%, the surface roughness is reduced by 60%-70%, and the battery performance is significantly improved, especially the improvement in cycle life and safety is particularly obvious. In addition, the test results under different positive electrode material systems all showed obvious improvement effects, which proved the versatility and adaptability of the method of the present invention.

[0184] 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 inhibiting the generation of aggregate particles on the surface of a positive electrode, characterized in that: The following steps are involved: S1. Raw material pretreatment: The positive electrode active material, conductive agent and binder are vacuum dried separately at a drying temperature of 60-90°C, a vacuum degree of -0.08-0.12 MPa, and a drying time of 2-4 hours; S2. Slurry preparation: The pretreated material is placed in a stirring tank equipped with a pulsed vortex generator according to a preset ratio. The pulse frequency is 20-50 Hz, the amplitude is 2-5 mm, and the stirring time is 30-60 minutes. At the same time, the stirring temperature is controlled within the range of 15-25°C by the temperature control system. S3. Ultrasonic dispersion treatment: The prepared slurry is introduced into an ultrasonic dispersion device with an ultrasonic power density of 300-600 W / L, a treatment time of 10-30 minutes, and a frequency of 40-60 kHz; S4, slurry filtration: the treated slurry is sequentially passed through filtration devices with filtration precisions of 5μm, 2μm and 1μm, and the filtration pressure is 0.2~0.5MPa; S5. Control before coating: Stir the filtered slurry evenly under the protection of inert gas and process it through a shear device with a shear rate of 800~1200s -1 , the processing time is 5~15 minutes.

2. The method for preparing particles for suppressing the generation of agglomerates on the surface of a positive electrode according to claim 1, wherein: The material to be dried in S1 is subjected to a magnetic separation purification treatment in advance, with a magnetic field strength of 0.5-1.5 T and 2-4 treatment times to remove ferromagnetic impurities in the material.

3. The method for preparing particles for suppressing the generation of agglomerates on the surface of a positive electrode according to claim 1, wherein: The inner wall of the stirring tank in S2 is made of ceramic material and is equipped with a magnetic metal ion capture device with a capture efficiency of ≥99.5%; And / or, the S2 slurry preparation process is carried out in a dry gas environment, the relative humidity of the environment is controlled at 5-15%, and the oxygen content is ≤100ppm.

4. The method for preparing particles for suppressing the generation of agglomerates on the surface of a positive electrode according to claim 1, wherein: The pulsed vortex generator in S2 is in a bidirectional alternating pulse mode, with a forward pulse to reverse pulse time ratio of 3:1 and a single pulse period of 2 to 5 seconds.

5. The method for preparing particles for suppressing the generation of agglomerates on the surface of a positive electrode according to claim 1, characterized in that: The ultrasonic dispersion device in S3 adopts gradient ultrasonic technology, with an initial ultrasonic power of 50% of the rated power, which is increased by 10% every 5 minutes until it reaches full power.

6. The method for preparing particles for suppressing the generation of agglomerates on the surface of a positive electrode according to claim 1, characterized in that: The filtering device in S4 includes a main filter and a bypass filter. The filtering accuracy of the bypass filter is one level higher than that of the main filter, and the bypass ratio is 20-30%. At the same time, an online particle monitoring device is set at the outlet of the filtering device. When the particle size is detected to be greater than 2μm, it automatically switches to full bypass filtering mode.

7. The method for preparing particles for suppressing the generation of agglomerates on the surface of a positive electrode according to claim 1, characterized in that: The S5 medium shear device adopts a programmable shear mode, including a low shear pre-adaptation stage, a medium shear transition stage and a high shear intensification stage; wherein the shear rate in the low shear pre-adaptation stage is 300~500s -1 , the time is 2 minutes, and the shear rate in the medium shear transition stage is 500~800s -1 The time is 3 minutes, and the shear rate of the high shear strengthening stage is 800~1200s -1 , the time is 5 to 10 minutes.

8. The method for preparing particles for suppressing the generation of agglomerates on the surface of a positive electrode according to claim 1, characterized in that: Before the S3 ultrasonic dispersion treatment, 0.1-0.5 wt% of a surfactant is added to the slurry, wherein the surfactant is one or a mixture of polyvinyl pyrrolidone, polyethylene glycol and polyoxyethylene ether; the added amount is calculated based on the total mass of the slurry.

9. The method for preparing particles for suppressing the generation of agglomerates on the surface of a positive electrode according to claim 1, characterized in that: It also includes S6, slurry online monitoring and correction: During the coating process, an online slurry agglomerate detection system is set up, using laser scattering detection technology. When it is detected that the agglomerate size is greater than 3μm or the number density exceeds 10 / cm², the slurry bypass ultrasonic redispersion device is automatically started, with an ultrasonic power of 400~600W and a processing time of 30~60 seconds. At the same time, the main line slurry flow rate is adjusted to reduce it by 10~20% until the detection indicators return to normal.

10. A positive electrode, characterized in that The invention is prepared by the preparation method for inhibiting the generation of agglomerate particles on the positive electrode surface according to any one of claims 1 to 9.

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