Slurry preparation and coating method and application of ultrathin pole piece

Abstract

The invention belongs to the technical field of lithium ion battery pole piece preparation, and discloses an ultrathin pole piece, a preparation method, a preparation system and application thereof, and a wet preparation process of slurry. The core comprises the following steps: preparing uniform slurry by adopting an improved wet process; a bisection continuous coating process is adopted, a continuous coating area and a reserved blank area are synchronously formed in the continuous movement of the current collector, and start-stop thickness fluctuation is eliminated; and the stability is guaranteed by constant liquid level control. According to the method, high-precision control over the thickness and the surface density of the pole piece can be achieved at low cost, consistency is good, and adaptability is high.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery manufacturing technology, specifically to a slurry preparation and coating method for ultrathin electrode sheets, and its application. Background Technology

[0002] Ultrathin electrodes (thickness less than 80μm) effectively shorten the lithium-ion transport path, reduce battery internal resistance, and enable faster charging and high-current discharging. Simultaneously, thinner electrodes exhibit less volume expansion / contraction during charging and discharging, reducing issues such as electrode cracking and active material shedding, thus improving battery durability. Ultrathin electrodes also facilitate lightweight and flexible batteries. The core of their high-quality fabrication lies in "uniform dispersion of the slurry" and "precise coating."

[0003] Currently, the mainstream preparation of ultrathin electrodes uses wet processes, among which coating techniques are mainly divided into two categories: (1) Slit extrusion coating: The slurry is extruded through a precision die, resulting in high coating uniformity, high consistency and high efficiency. However, the equipment is expensive, the requirements for slurry cleanliness are extremely high, and the production of electrode sheets of different specifications (width, thickness) requires the replacement of expensive custom dies, the changeover and debugging time is long, the flexible production capability is poor, resulting in high production costs for multiple types of products.

[0004] (2) Intermittent transfer coating: The slurry is indirectly transferred to the substrate through a transfer roller. This method has lower equipment costs, is flexible in changing equipment, and is suitable for multi-variety production and fragile substrates. However, during the start-up and shutdown phases of coating, the contact pressure and linear velocity between the transfer cylinder and the current collector change when the slurry is transferred, which can easily cause significant thickness fluctuations at the beginning and end of the coating (easily resulting in "thick edges and thin middle" or "striped unevenness"). For ultra-thin coatings, this thickness fluctuation is amplified (especially for ultra-thin electrodes of about 60μm, where the thickness tolerance is difficult to control within ±5μm), resulting in poor electrode surface density consistency and seriously affecting the uniformity of battery performance.

[0005] Furthermore, slurry preparation is a crucial preliminary step. Traditional slurry processes rely on empirical parameters, making it difficult to control the uniformity and stability of slurries for ultrathin electrodes with low solid content and high viscosity. These slurries are prone to sedimentation and agglomeration, further affecting coating uniformity and electrode quality.

[0006] Therefore, a contradiction exists in existing technologies: it is difficult to simultaneously achieve high consistency (slit coating) and low cost and high flexibility (intermittent transfer coating). This invention aims to provide a solution that can achieve coating uniformity and consistency comparable to slit coating while maintaining the low cost and high flexibility advantages of intermittent transfer coating. Summary of the Invention

[0007] This invention aims to overcome the shortcomings of the prior art and provide an ultra-thin lithium-ion battery electrode with precise thickness and uniform areal density, as well as its preparation method, preparation system, application, and wet preparation process of slurry. This method is low in cost, highly adaptable, and especially suitable for the production of various types of electrode sheets.

[0008] Firstly, to achieve the aforementioned objectives, this technical research involved monitoring and collecting data on viscosity and solid content during slurry mixing, plotting these data as curves, and performing fitting analysis. This revealed a strong correlation between the solid content and viscosity of the slurry. Therefore, this fitting analysis model can be used to controllably adjust the slurry viscosity under the same material system. Consequently, this invention employs the following technical solution: precisely controlling the feeding sequence and multi-stage variable-speed mixing to obtain a slurry with high uniformity and stable rheological properties.

[0009] A method for preparing slurry for ultrathin electrodes includes the following steps: S1. The binder and solvent are mixed and stirred at a first stirring speed to form a first mixture; S2. Add conductive slurry to the first mixture and mix the second mixture at the second stirring speed; S3. Add active material and conductive agent to the second mixture, and premix at the third stirring speed, at which point the mixture does not disperse; then disperse and stir at the fourth stirring speed to obtain a premixed slurry; S4. Vacuum mixing and defoaming treatment are performed on the premixed slurry obtained in step S3; The fourth stirring speed is higher than the second and third stirring speeds.

[0010] Preferably, as an improvement, the first stirring speed includes a main stirring speed of 40-50 rpm and a dispersing disc speed of 1800-2500 rpm, and the stirring time is 50-80 min; The second stirring speed is a main stirring speed of 30~50 rpm and a dispersing disc speed of 1200~1800 rpm, and the stirring time is 30~50 min; The third stirring speed is 25~40 rpm and the dispersing plate is not opened, and the stirring time is 30~50 min; The fourth stirring speed includes a main stirring speed of 40-50 rpm and a dispersion disc speed of 1800-2500 rpm, with a stirring time of 50-70 min.

[0011] Secondly, a method for preparing an ultrathin electrode sheet, wherein the slurry prepared using the above method is coated onto a current collector using the following method: The slurry is coated onto the current collector using a two-part continuous coating process. The coating is continuously applied on both sides of the length region corresponding to the future cutting of the electrode tabs, and a reserved blank area without slurry is formed in the length region. Both sides of the reserved blank area are continuously coated areas along the coating direction. The resulting wet electrode is dried and rolled to obtain an ultrathin electrode.

[0012] The key problem in studying traditional intermittent transfer coating technology lies in the fundamental reason for poor coating consistency and uniformity. This is because the intermittent coating process involves start-stop actions, which easily cause thickness fluctuations at the "coating-interval" junction. This causes changes in the contact pressure and linear velocity matching between the transfer cylinder and the collector during slurry transfer, resulting in thickness errors.

[0013] The two-part continuous coating process of this method simultaneously forms a continuous active material coating and a reserved tab blank area on the current collector during the continuous coating process, which fundamentally eliminates the thickness fluctuations caused by the start and stop of traditional intermittent coating.

[0014] Preferably, as an improvement, the two-part continuous coating process is implemented in the following way: The transfer roller of the coating machine rotates continuously at a constant speed. Its surface structure and motion trajectory are set so that when the current collector passes through at a constant speed, a continuous coating pattern with a preset width of blank area is automatically formed on the surface of the current collector.

[0015] By maintaining a close connection between the continuous coating transfer cylinder and the current collector, the start-up and shutdown process of the intermittent coating process is eliminated. The contact pressure and linear velocity matching between the transfer cylinder and the current collector do not change, achieving the effect of uniform surface density and increasing the consistency of the electrode sheets.

[0016] Preferably, as an improvement, step S2 employs the principle of a car fuel tank buoy to maintain a stable slurry level in the coating machine's feed tank. The car fuel tank buoy principle enables constant liquid level supply control, ensuring extreme stability of the slurry supply during the coating process.

[0017] Thirdly, a preparation system for implementing the method for preparing the ultrathin electrode of the lithium-ion battery, comprising: The slurry preparation unit is equipped with a dual-speed stirring device that can control the rotation speed of the main stirrer and the dispersion disc; The coating unit includes a coating head mechanism capable of performing two-part continuous coating; The constant liquid level feeding unit includes a closed-loop control system for maintaining a stable liquid level in the coating unit's tank; it is designed based on the principle of a buoy in an automotive fuel tank. Drying and rolling unit.

[0018] Preferably, as an improvement, the coating head mechanism includes a transfer roller for coating a continuous coating zone.

[0019] Preferably, as an improvement, the closed-loop control system includes a controller, a float electrically connected to the controller, the float floating on the liquid surface in the coating unit tank, and the controller is also electrically connected to the coating head mechanism.

[0020] By acquiring correlation curves based on liquid level, coating speed, coating speed ratio, and areal density, and studying each factor, stable and uniform coating equipment parameters were confirmed. The liquid level is stably controlled using the buoyancy principle, increasing coating stability and areal density uniformity, reducing the impact of liquid level. Simultaneously, the coating head mechanism achieves intelligent feeding, reducing manual intervention and increasing production efficiency.

[0021] Fourthly, an ultrathin electrode sheet for lithium-ion batteries is prepared by the method described above. This ultrathin electrode sheet exhibits excellent thickness uniformity and areal density consistency.

[0022] Fifthly, the aforementioned ultrathin electrode sheet for lithium-ion batteries is used in the preparation of lithium-ion batteries.

[0023] The present invention has the following beneficial effects: 1. Through the synergistic optimization of processes and systems, precise control of the thickness of ultra-thin electrode sheets (e.g., 65μm) by ±2μm has been achieved. After continuous coating of hundreds of meters (e.g., 220 meters), the density error is less than 1.5%, which greatly improves the consistency of the battery.

[0024] 2. The two-part continuous coating process provided by this invention increases the coating speed by about 7 times; the optimized slurry preparation process shortens the stirring time by about 25%; the system does not require frequent replacement of expensive dies for different specifications, and the overall production cost is significantly reduced.

[0025] 3. Strong adaptability and flexibility: The system and method are highly adaptable to different slurry types, electrode sizes and thicknesses, making them particularly suitable for flexible production needs with multiple varieties and small batches.

[0026] 4. High yield: Stable slurry and precise coating process reduce defects such as electrode breakage and pinholes. Combined with intelligent control of constant liquid level feeding, it improves the stability of the production process and the yield. Attached Figure Description

[0027] Figure 1 The images show SEM images of the electrodes in Comparative Example 1 and Example 1.

[0028] Figure 2 The curves and fitting curves show the correlation between the solid content and viscosity of the slurry; the left graph represents the positive electrode, and the right graph represents the negative electrode.

[0029] Figure 3The diagram shows the intermittent coating method in Comparative Example 2 and the continuous coating principle in Comparative Example 2 in Example 3 of the present invention; in the diagram, A represents the blank area and B represents the coated area.

[0030] Figure 4 The curves show the correlation between liquid level, coating speed, coating speed ratio, and areal density.

[0031] Figure 5 This is a schematic diagram of the liquid level control principle.

[0032] Figure 6 This is a diagram showing the surface density error of the positive and negative electrodes on both sides in Comparative Example 1.

[0033] Figure 7 This is a diagram showing the surface density error of the positive and negative electrodes on one or both sides in Example 1. Detailed Implementation

[0034] The following detailed description illustrates the specific implementation method: Example 1: The improved wet slurry preparation process of the present invention includes the following steps: (1) Add the binder and solvent to the mixer and stir at 45 rpm and 2000 rpm for 60 min.

[0035] (2) Add conductive paste and stir at 40 rpm and 1500 rpm for 40 min.

[0036] (3) Add all the active material and conductive agent into the stirrer and stir at 30 rpm for 40 min (without dispersing).

[0037] (4) Stir at 45 rpm and 2000 rpm for 60 min, and turn on the circulating water and vacuum during the stirring.

[0038] (5) Defoaming: stirring speed 10 rpm, time 20 min.

[0039] Based on this method, the viscosity and solid content of the positive and negative electrode slurries were monitored and collected during the slurry mixing process, and then plotted as curves for fitting analysis, as follows: Figure 2 As shown, its solid content is strongly correlated with its viscosity, which allows for the controllable adjustment of slurry viscosity using this fitting analysis model under the same material system.

[0040] Comparative Example 1: Traditional Slurry Preparation Process (1) Add the binder and solvent to the mixer and stir at 45 rpm and 2000 rpm for 60 min.

[0041] (2) Add conductive agent, stir at 25 rpm for 20 min (without dispersing), scrape the material, and then stir at 40 rpm for 40 min.

[0042] (3) Add conductive paste and stir at 40 rpm and 1500 rpm for 40 min.

[0043] (4) Add the active material in three batches, stir at 25 rpm for 20 min (without dispersing), scrape the material, and then stir at 40 rpm and 1500 rpm for 40 min.

[0044] (4) Stir at 45 rpm and 2000 rpm for 60 min, and turn on the circulating water and vacuum during the stirring.

[0045] (5) Defoaming: stirring speed 10 rpm, time 20 min.

[0046] pass Figure 1 The SEM images of the electrodes show that the ultrathin electrodes produced using Example 1 and Comparative Example 2 did not exhibit significant changes, with the conductive agent uniformly distributed around the active material. However, compared to Example 1, the method reduced the stirring time by 25%, increasing production efficiency.

[0047] Example 2: Through research Figure 4 The relevant parameters in the correlation curves shown, including liquid level, coating speed, coating speed ratio, and areal density, confirm the equipment parameters for stable and uniform coating. Then, a system for preparing ultrathin lithium-ion battery electrodes is provided, comprising: The slurry preparation unit is equipped with a dual-speed mixing device (existing dual planetary mixer) that can control the rotation speed of the main mixer and the dispersion disc. The coating unit, the core of which is the modified intermittent coating machine, has a key innovation in the coating head mechanism, which is used to achieve "two-part continuous coating". This includes the coating head mechanism for achieving two-part continuous coating - the transfer roller. Its surface structure and motion trajectory are set so that when the current collector passes through at a constant speed, it automatically forms a continuous coating pattern on the surface of the current collector with a preset width of blank area.

[0048] The constant liquid level feeding unit uses the principle of a car fuel tank buoy to maintain a stable liquid level in the coating machine's slurry tank. It includes a slurry transfer tank, a delivery pump, and a core liquid level stability control subsystem. The structure and principle of this subsystem are as follows: Figure 5 As shown, it specifically includes: Float and sensing mechanism: such as Figure 5 As shown, a corrosion-resistant float is floating on the surface of the slurry in the coating machine's trough.

[0049] Controller: A programmable logic controller (PLC) is used. The float is connected to a high-precision potentiometer or telescopic displacement sensor, which converts the liquid level signal into an electrical signal and transmits it to the PLC in real time.

[0050] Actuator: The PLC is electrically connected to the slurry delivery pump. The PLC pre-stores the target liquid level value and dynamically adjusts the pump speed or switching time based on the deviation between the real-time liquid level and the target liquid level, thereby achieving automatic and precise slurry replenishment. This system can control the slurry level fluctuation in the coating tank within ±0.5 mm, which is far superior to the accuracy of manual or simple on / off control.

[0051] Drying and rolling unit (same as prior art).

[0052] Example 3: An ultrathin electrode for a lithium-ion battery and its preparation method, comprising the following steps: S1. Slurry preparation: The electrode slurry prepared in Example 1 was used; S2. Electrode Coating: Using the system of Example 3, a two-part continuous coating process is implemented to coat the battery slurry onto the current collector. Continuous coating is performed on both sides of the length region corresponding to the future cutting of the electrode tab, and a reserved blank area without slurry is formed in the length region. Both sides of the reserved blank area along the coating direction are continuous coating areas, resulting in a wet electrode. S3. Drying and rolling: The wet electrode sheet is dried and rolled to obtain an ultrathin electrode sheet.

[0053] Comparative Example 2: The electrode paste prepared in Comparative Example 1 was used to coat the electrode sheet using a traditional process.

[0054] The electrode sheets prepared in Example 3 and Comparative Example 2 are as follows: Figure 3 As shown, the two-part continuous coating process in Example 3 can reserve blank areas in the middle and on both sides for the intermittent coating process, which facilitates the cutting of the tabs. By closely connecting the continuous coating transfer cylinder with the current collector, the start-up and stop process of the intermittent coating process is eliminated. The contact pressure and linear velocity matching degree between the transfer cylinder and the current collector do not change, achieving the effect of uniform surface density and increasing the consistency of the electrode sheets.

[0055] This invention improves and optimizes the slurry preparation and coating processes. Example 1, while maintaining slurry uniformity, reduces slurry preparation time by 25%, and simultaneously improves coating surface density uniformity, continuity, and efficiency. Under 220-meter continuous coating, the surface density error is only 1.5%, and the coating speed is increased by 7 times. In contrast, Comparative Example 1 has a surface density error of 7.6%. Figure 6 , Figure 7 This is a diagram showing the surface density error of the single and double sides of the electrode in Comparative Example 2 and Example 3.

[0056] The above descriptions are merely embodiments of the present invention, and common knowledge such as specific technical solutions and / or characteristics are not described in detail here. It should be noted that those skilled in the art can make various modifications and improvements without departing from the technical solutions of the present invention, and these should also be considered within the scope of protection of the present invention. These modifications and improvements will not affect the effectiveness of the implementation of the present invention or the practicality of the patent. The scope of protection claimed in this application should be determined by the content of its claims, and the specific embodiments described in the specification can be used to interpret the content of the claims.

Claims

1. A method for preparing a slurry for ultrathin electrodes, characterized in that, Includes the following steps: S1. The binder and solvent are mixed and stirred at a first stirring speed to form a first mixture; S2. Add conductive slurry to the first mixture and mix the second mixture at the second stirring speed; S3. Add active material and conductive agent to the second mixture, and premix at the third stirring speed, at which point the mixture does not disperse; then disperse and stir at the fourth stirring speed to obtain a premixed slurry; S4. Vacuum mixing and defoaming treatment are performed on the premixed slurry obtained in step S3; The fourth stirring speed is higher than the second and third stirring speeds.

2. The method for preparing slurry for ultrathin electrodes according to claim 1, characterized in that: The first stirring speed includes a main stirring speed of 40~50 rpm and a dispersion disc speed of 1800~2500 rpm, and the stirring time is 50~80 min; The second stirring speed is a main stirring speed of 30~50 rpm and a dispersing disc speed of 1200~1800 rpm, and the stirring time is 30~50 min; The third stirring speed is 25~40 rpm and the dispersing plate is not opened, and the stirring time is 30~50 min; The fourth stirring speed includes a main stirring speed of 40-50 rpm and a dispersion disc speed of 1800-2500 rpm, with a stirring time of 50-70 min.

3. A method for preparing an ultrathin electrode, characterized in that, The slurry prepared using the method described in claim 1 or 2 is coated onto the current collector using the following method: The slurry is coated onto the current collector using a two-part continuous coating process. The coating is continuously applied on both sides of the length region corresponding to the future cutting of the electrode tabs, and a reserved blank area without slurry is formed in the length region. Both sides of the reserved blank area are continuously coated areas along the coating direction. The resulting wet electrode is dried and rolled to obtain an ultrathin electrode.

4. The method for preparing an ultrathin electrode sheet according to claim 3, characterized in that: The two-part continuous coating process is achieved in the following way: The transfer roller of the coating machine rotates continuously at a constant speed. Its surface structure and motion trajectory are set so that when the current collector passes through at a constant speed, a continuous coating pattern with a preset width of blank area is automatically formed on the surface of the current collector.

5. The method for preparing an ultrathin electrode sheet according to claim 4, characterized in that: In step S2, the principle of a car fuel tank buoy is used to maintain the stability of the slurry level in the coating machine's trough.

6. A system for preparing ultrathin electrodes for carrying out the method of claim 5, characterized in that, include: The slurry preparation unit is equipped with a dual-speed stirring device that can control the rotation speed of the main stirrer and the dispersion disc; The coating unit includes a coating head mechanism capable of performing two-part continuous coating; The constant liquid level feeding unit includes a closed-loop control system for maintaining a stable liquid level in the coating unit's tank. Drying and rolling unit.

7. The preparation system according to claim 6, characterized in that, The coating head mechanism includes a transfer roller for coating a continuous coating area.

8. The preparation system according to claim 7, characterized in that: The closed-loop control system includes a controller, a float electrically connected to the controller, the float floating on the liquid surface in the coating unit tank, and the controller is also electrically connected to the coating head mechanism.

9. An ultrathin electrode sheet for a lithium-ion battery, characterized in that: It is prepared by the method described in claim 3.

10. The ultrathin electrode sheet for lithium-ion batteries according to claim 9 is used to prepare lithium-ion batteries.

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