Method and equipment for mixing powder

Abstract

The invention provides a method and equipment for mixing powder. The method comprises the following steps: pretreating a material and introducing a liquid phase; dynamically shearing and dispersing; gradient heating and solvent evaporation; performing high-speed shearing to trigger fibrosis; the fiber structure is optimized through low-speed kneading; crushing the fiberized material; according to the method, a low-boiling-point solvent is introduced in the powder dry mixing process through a liquid-phase-assisted dry mixing-low-temperature solvent recovery-controllable fibration synergistic process, the powder mixing efficiency and uniformity are improved through a liquid phase, and after powder is mixed uniformly, condensate water of a stirring tank is closed, so that the temperature of a slurry intermediate semi-finished product is increased; and the stirring tank is synchronously vacuumized, so that the low-boiling-point solvent is boiled, low-boiling-point solvent steam is pumped into the condensation system, and the low-boiling-point solvent is recycled, so that uniformly mixed dry powder is obtained.

Description

Technical Field

[0001] The present invention relates to the field of lithium ion batteries, and in particular to a method and equipment for mixing powders. Background Art

[0002] In recent years, with the intensification of global energy shortages and environmental pollution, the search for sustainable and biodegradable biomass energy to replace oil has become a global consensus. Against this backdrop, new energy vehicles, particularly electric vehicles, have experienced rapid development due to their low emissions, high efficiency, and environmentally friendly characteristics. As the core of new energy vehicles, battery technology is a common goal for optimizing both performance and cost. Currently, the positive and negative electrodes of batteries are typically produced using a wet coating process. While this method has been optimized and is relatively mature, it still suffers from high maintenance costs and labor requirements associated with homogenization, baking, and NMP recovery.

[0003] Compared to wet coating processes, dry electrode preparation technology is attracting increasing attention from companies due to its environmental and cost-effectiveness. Dry electrodes utilize the fibrillation effect of adhesives to bond active materials together, forming a self-supporting film. This eliminates the need for solvents, simplifies the electrode preparation process, and reduces manufacturing costs. Dry processes not only increase the energy density of electrodes but also enhance the cycle performance and stability of batteries, making them a new development direction for the lithium battery industry.

[0004] The commercial application of dry electrode technology still faces technical and engineering challenges, including the uniform dispersion of active material particles, the stability of the dry mixing process, and the mechanical strength of the film.

[0005] To this end, we propose a powder mixing method and equipment to solve the problem of insufficient mixing uniformity between the conductive agent and the main material. Summary of the Invention

[0006] The purpose of the present invention is to solve the shortcomings of the prior art. In order to achieve the above purpose, the present invention adopts the following technical solutions: A method for mixing powders, comprising the following steps: S1: Material pretreatment and liquid phase introduction: adding the active material, conductive agent, and binder to a solvent with a boiling point lower than 100° C. and a surface tension lower than that of the active material; S2: Dynamic shear dispersion: Start liquid phase mixing to evenly disperse the conductive agent and binder on the surface of the active material powder; S3: Gradual temperature increase and solvent evaporation; the condensation system is closed and the cabin is evacuated, causing the solvent to boil into steam and enter the solvent recovery system; S4: High-speed shear triggers fiberization; when the solvent is removed to a residual amount of ≤0.5wt%, the stirring blade speed is increased to fiberize the powder in the chamber; S5: kneading at low speed to optimize the fiber structure; after the powder is fiberized, the stirring speed is reduced and the fiberized powder is kneaded to further improve the fiberization degree of the powder; S6: pulverizing the fibrous material; after the powder kneading is completed, the obtained powder is pulverized to obtain a uniformly dispersed fibrous material.

[0007] Further preferably, in step S1, the active material, the conductive agent and the binder are added to a mixing bin according to a mass ratio to obtain a powder, a solvent is injected through an atomizing spray system, the mass ratio of the solvent to the powder is 1:10-1:20, and premixing is performed by stirring.

[0008] Further preferably, the liquid phase mixing in step S2 includes multi-stage shear control and real-time monitoring feedback, wherein the multi-stage shear control is to form a shear flow field in a solvent wetting environment by linking a high-speed shear paddle with a vortex generator; and the real-time monitoring feedback is to monitor the mixing uniformity through an online resistivity sensor and a near-infrared spectrometer.

[0009] Further preferably, in step S3, the vacuum degree is ≤10 kPa and the solvent recovery rate is ≥98%.

[0010] Further preferably, the rotation speed of the shearing stirring blade in step S4 is 30-60 m / s.

[0011] More preferably, in step S5, the kneading speed is 500-1000 rpm and the kneading temperature is 60-80°C.

[0012] A device for mixing powders, comprising: A stirring tank, wherein the mixed powder and the auxiliary liquid are contained in the stirring tank, a discharge port is opened at the lower left end of the stirring tank, and the outer wall of the stirring tank is covered with a cooling jacket; A stirring device, comprising a motor and a paddle, wherein the motor is mounted on the hatch of the stirring tank and connected to the paddle in the stirring tank via a connecting shaft; A cooling device, comprising a cooling system and a steam condenser disposed in the cooling system, wherein the steam condenser is connected to the stirring tank via a steam recovery pipe; A vacuum pumping device is installed on the side of the cooling device and is connected to the cooling system.

[0013] Further preferably, a thermometer is installed in the stirring tank.

[0014] Further preferably, a hatch lifting device is installed on the side of the mixing tank.

[0015] Compared with the prior art, the present invention has the following beneficial effects: The present invention adopts the collaborative process of liquid-phase assisted dry mixing-low-temperature solvent recovery-controllable fiberization, introduces a low-boiling-point solvent during the powder dry mixing process, and improves the efficiency and uniformity of powder mixing through the liquid phase. After the powder is evenly mixed, the condensed water in the stirring tank is turned off to increase the temperature of the semi-finished product in the slurry; and simultaneously vacuumizes the stirring tank to boil the low-boiling-point solvent, and the low-boiling-point solvent vapor is pumped into the condensation system to recover the low-boiling-point solvent, thereby obtaining a uniformly mixed dry powder.

[0016] The present invention avoids the high-energy-consuming high-temperature baking process. After most of the low-boiling-point solvent is recovered, the dry powder is subjected to high-speed shearing for fiberization. This solution solves the core problems of uneven dispersion of conductive agents and high energy consumption in dry mixtures through the synergistic mechanism of liquid phase wetting and low-temperature recovery, providing a quantifiable process path for the preparation of dry electrodes for high-energy-density batteries. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 This is a flow chart of liquid-assisted dry mixing-low-temperature solvent recovery-controllable fiberization; Figure 2 This is a schematic diagram of the liquid-assisted dry mixing equipment; Figure 3 is the diaphragm resistance curve; Figure 4 It is a scatter plot of battery cell rate performance.

[0018] In the figure: discharge port 1, cooling jacket 2, mixed powder 3, auxiliary liquid 4, high-speed dispersing paddle 1 5, thermometer 6, dispersing motor 1 7, stirring motor 8, dispersing motor 2 9, high-speed dispersing paddle 2 10, stirring paddle 11, hatch lifting device 12, steam recovery pipe 13, steam condensing pipe 14, cooling system 15, vacuum device 16. DETAILED DESCRIPTION

[0019] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments.

[0020] Reference Figures 1-4 , a method for mixing powders, comprising the following steps: S1: adding an active material, a conductive agent, and a binder to a solvent, wherein the boiling point of the solvent is lower than 100° C. and the surface tension of the solvent is lower than the surface tension of the active material; In this example, active materials (such as NCM811, LFP graphite, or silicon-carbon anode particles), conductive agents (carbon black SP, CNT), and binder (PTFE, PVDF, CMC, PAA, etc. powders) are added to a stirring tank in the appropriate mass ratio. For liquid phase introduction, a low-boiling-point solvent (such as ethanol, acetone, or a fluorinated ether with a boiling point <100°C) is selected, with a surface tension below the critical wetting tension of the active material (e.g., NCM has a surface energy of approximately 50 mN / m and acetone has a surface tension of 23 mN / m). The solvent is injected via an atomizing spray system at a solvent-to-powder mass ratio of 1:15. A stirrer (200-500 rpm) is activated for premixing, and a centrifugal force gradient is used to uniformly coat the particle surface with the solvent. An ultrasonic module (20 kHz frequency) is simultaneously activated to break up micron-sized agglomerates of the conductive agent, improving dispersion uniformity.

[0021] S2: Start liquid phase mixing to evenly disperse the conductive agent and binder on the surface of the active material powder; In the embodiment, a dual planetary high-speed shearing paddle (rotation speed 5000-10000 rpm) is activated in conjunction with a vortex generator (central stirring paddle) in a solvent wetting environment. The solvent liquid phase is utilized to reduce shear heat accumulation (the temperature in the stirring tank is controlled at 5-40°C). The shear flow field and capillary force act synergistically to embed conductive agent nanoparticles (e.g., carbon black D50 ≤ 50 nm) into the gaps between the main material particles, forming a "core-shell" structured composite powder. The mixing uniformity is monitored using an online resistivity sensor (detection accuracy ±5%) and a near-infrared spectrometer (NIR). Mixing is determined to be complete when the resistivity coefficient of variation (CV value) is ≤5% and the standard deviation of the NIR spectral peak intensity is ≤3%.

[0022] S3: Close the condensation system and evacuate the cabin, causing the solvent to boil into steam and enter the solvent recovery system; In this embodiment, the condensation system is turned off, and the temperature inside the tank is raised to above the boiling point of the solvent (e.g., 56°C for acetone). Simultaneously, a vacuum pump is activated (vacuum level ≤ 10 kPa), and the vaporized solvent is introduced into a condensation recovery system (condensation can be performed using a refrigerator or liquid nitrogen, etc.), with a solvent recovery rate of ≥ 98%. The amount of solvent removed is monitored using a mass flow meter, and fiberization is initiated when the residual amount is ≤ 0.5 wt%.

[0023] S4: When the solvent is removed to a residual amount of ≤0.5wt%, the stirring blade speed is increased to fiberize the powder in the cabin; In the embodiment: when the solvent is removed to a residual amount of ≤0.5 wt%, the high-speed shear mode is switched to trigger fiberization using the mechanical energy of the PTFE binder: under the action of shear force, the PTFE particles (initial particle size 100-200 μm) are stretched into a fiber network with a diameter of 50-200 nm, entangled with the active material and the conductive agent to form a three-dimensional conductive skeleton. At the same time, the accompanying temperature increase further dries the residual solvent in the material.

[0024] S5: After the powder is fiberized, the stirring speed is reduced and the fiberized powder is kneaded to further improve the fiberization degree of the powder; In the embodiment: kneading parameter settings: reduce the rotation speed to 500-1000 rpm to enhance the fiber winding strength through shear-extrusion action; control the kneading temperature at 60-80°C; the kneading stage lasts for 10-20 minutes to form an "interpenetrating" structure between the fiber network and the active material and the conductive agent, thereby improving the mechanical strength of the electrode.

[0025] S6: After the powder kneading is completed, the obtained powder is crushed to obtain a uniformly dispersed fibrous material.

[0026] In the embodiment, the fiberized material after kneading is crushed at a relatively high speed and the D50 of the material is controlled to be 0.2-3 mm to ensure uniform film formation of the electrode.

[0027] In step S1, active material, conductive agent and binder are added to a mixing bin according to a mass ratio to obtain powder, and a solvent is injected through an atomizing spray system. The mass ratio of the solvent to the powder is 1:10-1:20, and the mixture is premixed by stirring.

[0028] In this embodiment, the active material is one of NCM811, LFP graphite, or silicon-carbon anode particles; the conductive agent is carbon black SP or CNT; and the binder is one or more of PTFE, PVDF, CMC, or PAA. A solvent with a boiling point below 100°C (such as acetone, ethanol, or a fluorinated ether) is selected, and its surface tension must be lower than the critical wetting tension between the conductive agent and the main material (for example, carbon black has a surface energy of approximately 30 mN / m, and NCM has a surface energy of approximately 50 mN / m). Solvent is injected into the mixing chamber via a negative pressure atomization spray system, with a solvent to powder mass ratio of 1:15, ensuring the formation of a monolayer liquid film on the powder surface, reducing van der Waals forces and inhibiting agglomeration of the conductive agent.

[0029] The liquid phase mixing in step S2 includes multi-stage shear control and real-time monitoring feedback. The multi-stage shear control is to form a shear flow field in a solvent wetting environment by linking a high-speed shear paddle with a vortex generator; the real-time monitoring feedback is to monitor the mixing uniformity through an online resistivity sensor and a near-infrared spectrometer.

[0030] Step S3 includes vacuum extraction and condensation recovery and residual solvent control. The vacuum extraction and condensation recovery are to close the condensation system to raise the warehouse temperature to above the boiling point of the solvent; synchronously start the vacuum pump to introduce the vaporized solvent into the condensation recovery system; the residual solvent control is to monitor the solvent removal amount through a mass flow meter.

[0031] In step S4, the shearing stirring blade has a rotation speed of 30-60 m / s, and the shear force is used to stretch the PTFE particles (initial particle size 100-200 μm) to form a fiber network with a diameter of 50-200 nm.

[0032] In step S5, the kneading speed is 500-1000 rpm, the kneading temperature is 60-80°C, and the kneading stage lasts for 10-20 minutes, so that the fiber network, active material and conductive agent form an "interpenetrating" structure, thereby improving the mechanical strength of the electrode.

[0033] The present invention solves the core problems of uneven dispersion of conductive agents and high energy consumption in dry mixtures through the synergistic mechanism of liquid phase wetting and low-temperature recovery, and provides a quantifiable process path for the preparation of dry electrodes for high-energy-density batteries.

[0034] The beneficial effects of the present invention are: Energy recycling: The latent heat released by solvent condensation is fed back to the electrode hot roller heating system through a heat exchanger, reducing external heating energy consumption (comprehensive energy consumption is reduced by more than 60% compared with traditional drying processes).

[0035] Modular design of the equipment: The mixing chamber integrates temperature control, vacuum, shearing and monitoring units to achieve integrated continuous production of "mixing-desolventization-fiberization".

[0036] Conductive agent dispersion optimization: The solvent liquid phase reduces the energy barrier for carbon black agglomeration, and the density of its contact points with the main material is increased by more than 30%, and the fluctuation rate of the electrode surface resistance is ≤8%.

[0037] Process compatibility: Applicable to moisture-sensitive material systems such as high-nickel ternary and silicon-carbon anodes, and the solvent recovery system can adapt to different media such as low-boiling point alcohols, ethers, and water.

[0038] A device for mixing powders, comprising: A stirring tank (also called a mixing tank) is provided with a mixed powder 3 and an auxiliary liquid 4 (a low-boiling-point solvent). A discharge port 1 is provided at the lower left end of the stirring tank, and a cooling jacket 2 is provided on the outer wall of the stirring tank. A stirring device, comprising a motor and a paddle, wherein the motor is mounted on the hatch of the stirring tank and connected to the paddle in the stirring tank via a connecting shaft; In the embodiment: the motor includes a dispersion motor 7, a stirring motor 8, and a dispersion motor 2 9. The stirring motor 8 is installed between the dispersion motor 1 7 and the dispersion motor 2 9. The paddle includes a high-speed dispersion paddle 5, a high-speed dispersion paddle 2 10 and a stirring paddle 11. The high-speed dispersion paddle 5, the high-speed dispersion paddle 2 10 and the stirring paddle 11 are respectively connected to the dispersion motor 1 7, the dispersion motor 2 9 and the stirring motor 8 through connecting shafts. The paddle is driven by the motor to rotate to achieve the effect of mixing and stirring the mixed powder 3 and the auxiliary liquid 4.

[0039] A cooling device, comprising a cooling system 15 and a steam condenser 14 disposed within the cooling system 15, wherein the steam condenser 14 is connected to the stirring tank via a steam recovery pipe 13; In the embodiment, the temperature in the stirring tank can be controlled by a cooling device so that the temperature in the tank is controlled at 5-40°C. The condensation method can be a refrigerator or liquid nitrogen.

[0040] The vacuum pumping device 16 is installed on the side of the cooling device and is connected to the cooling system.

[0041] In the embodiment, the vacuum degree is set to ≤10 kPa by the vacuum pump 16, and the vaporized solvent is introduced into the cooling device to make the solvent recovery rate ≥98%.

[0042] A thermometer 6 is installed in the stirring tank.

[0043] In the embodiment: the temperature in the stirring tank is monitored in real time by the thermometer 6.

[0044] A hatch lifting device 12 is installed on the side of the mixing tank.

[0045] In the embodiment, the hatch of the mixing tank is opened by the hatch lifting device 12 to facilitate the addition of the mixed powder 3 and the auxiliary liquid 4 into the mixing tank.

[0046] The following tests were conducted on the membranes prepared in the examples and comparative examples. Comparative Example 1: Traditional dry mixing-dry film forming and composite group (traditional dry mixing-dry coating) Raw material system: Active material: negative electrode graphite material, particle size D50 about 10μm; Conductive agent: conductive carbon black (SP) accounts for 2% by mass; Binder: PTFE powder (2%); Process characteristics: Dry mixing: Use a powerful mixer (speed 500-800 rpm) to premix the active substance, conductive agent, and PTFE dry powder, and achieve initial dispersion through mechanical shear force.

[0047] 2. Fiberization: Use a dual high-speed shearing device (rotation speed 12000-15000 rpm) to form a fiber network with a diameter of 50-200 nm at 30-60°C.

[0048] 3. Calendering film: The fibrous material is pressed into a 100μm self-supporting film by a multi-roll calender (roll gap accuracy 0.001 mm), and then combined with the current collector (copper foil) by a 5-roll or 10-roll laminator.

[0049] Example 1: Liquid-assisted high-efficiency mixing-dry film formation and composite group (high-efficiency mixing-dry coating) Raw material system: Active material / conductive agent: same as traditional dry mix group; Binder: PTFE, PVDF, PAA; Dispersion medium: low boiling point solvent (acetone), the dosage is 1 / 15-1 / 20 of the powder mass; Process characteristics: 1. Liquid phase premixing: The powder is mixed with the solvent in a planetary mixer (200-500 rpm), the solvent is used to wet and reduce agglomeration, and the conductive agent agglomerates are broken up by simultaneous ultrasonic treatment (20 kHz).

[0050] 2. Vacuum desolventization: 98% of the solvent was recovered by gradient heating (5°C / min) and vacuum system (≤10 kPa), and the residual amount was controlled below 0.5 wt%.

[0051] 3. Dry film forming: After desolventization, the material enters the fiberization stage, and the process is similar to the traditional dry mixing group.

[0052] Comparative Example 2: Wet Mixing and Coating Group (Wet Coating) Raw material system: Active material / conductive agent: same as the previous two groups; Binder: PAA and SBR account for 2%; Solvent: water, the amount is 40-60% of the total mass of the slurry; Thickener: carboxymethyl cellulose (CMC); Process characteristics: 1. Preparation of adhesive solution: Dissolve CMC in water to form 5-10% adhesive solution, and add CMC to adjust the viscosity.

[0053] 2. Wet homogenization: Add the conductive agent and active material step by step, and disperse them in a double planetary mixer (revolution 25 rpm / rotation 1200 rpm) for 2-3 hours. The solid content of the slurry is controlled at 60-70%.

[0054] 3. Coating and drying: Use comma scraper or slit extrusion coating, 150-200℃ hot air drying, solvent recovery rate must be ≥95%.

[0055] The above-made diaphragm was tested for resistance and rate performance. The test data are as follows: Figure 3 and Figure 4 As shown; experimental results show that the electrode prepared by liquid-phase assisted-dry method achieves a level of rate performance comparable to that of wet-coated electrode (3C capacity retention rate is close to 100%). The key lies in the liquid-phase assisted mixing technology of low-boiling point solvents, which effectively breaks the agglomeration of conductive agents (such as carbon nanotubes and carbon black) and forms a uniform three-dimensional conductive network, while avoiding the conductive network breakage problem caused by insufficient mechanical shear dispersion in traditional dry process; in contrast, the capacity retention rate of traditional dry-process electrode at 3C rate is only 83% of that of wet process due to uneven dispersion of conductive agent (coverage rate is only 40%-60%) and insufficient dispersion of PTFE; therefore, the liquid-phase assisted-dry process retains the low energy consumption advantage of dry method while optimizing the conductive / adhesive system through liquid phase premixing and vacuum desolventizing technology (residual solvent <0.5 wt%), providing a feasible path for high-rate and low-cost battery manufacturing.

[0056] The present invention adopts the collaborative process of liquid-phase assisted dry mixing-low-temperature solvent recovery-controllable fiberization, introduces a low-boiling-point solvent during the powder dry mixing process, and improves the efficiency and uniformity of powder mixing through the liquid phase. After the powder is evenly mixed, the condensed water in the stirring tank is turned off to increase the temperature of the semi-finished product in the slurry; and simultaneously vacuumizes the stirring tank to boil the low-boiling-point solvent, and the low-boiling-point solvent vapor is pumped into the condensation system to recover the low-boiling-point solvent, thereby obtaining a uniformly mixed dry powder.

[0057] The present invention avoids the high-energy-consuming high-temperature baking process. After most of the low-boiling-point solvent is recovered, the dry powder is subjected to high-speed shearing for fiberization. This solution solves the core problems of uneven dispersion of conductive agents and high energy consumption in dry mixtures through the synergistic mechanism of liquid phase wetting and low-temperature recovery, providing a quantifiable process path for the preparation of dry electrodes for high-energy-density batteries.

[0058] The present invention breaks through the dual bottlenecks of dry mixing uniformity and energy consumption through the synergistic mechanism of liquid phase assistance and low-temperature recovery, providing a key technical path for the industrialization of the next generation of high-energy density batteries.

Claims

1. A method for mixing powders, characterized in that: Here are the steps: S1: adding an active material, a conductive agent, and a binder to a solvent, wherein the boiling point of the solvent is lower than 100° C. and the surface tension of the solvent is lower than the surface tension of the active material; S2: Start liquid phase mixing to evenly disperse the conductive agent and binder on the surface of the active material powder; S3: Close the condensation system and evacuate the cabin, causing the solvent to boil into steam and enter the solvent recovery system; S4: When the solvent is removed to a residual amount of ≤0.5wt%, the stirring blade speed is increased to fiberize the powder in the cabin; S5: After the powder is fiberized, the stirring speed is reduced and the fiberized powder is kneaded; S6: After the powder kneading is completed, the obtained powder is crushed to obtain a uniformly dispersed fibrous material.

2. A method for mixing powders according to claim 1, characterized in that: In step S1, active material, conductive agent and binder are added to a mixing bin according to a mass ratio to obtain powder, and a solvent is injected through an atomizing spray system. The mass ratio of the solvent to the powder is 1:10-1:20, and the mixture is premixed by stirring.

3. The method for mixing powders according to claim 1, wherein: The liquid phase mixing in step S2 includes multi-stage shear control and real-time monitoring feedback. The multi-stage shear control is to form a shear flow field in a solvent wetting environment by linking a high-speed shear paddle with a vortex generator; the real-time monitoring feedback is to monitor the mixing uniformity through an online resistivity sensor and a near-infrared spectrometer.

4. The method for mixing powders according to claim 1, wherein: In step S3, the vacuum degree is ≤10 kPa, and the solvent recovery rate is ≥98%.

5. The method for mixing powders according to claim 1, wherein: The rotation speed of the shearing stirring blade in step S4 is 30-60 m / s.

6. The method for mixing powders according to claim 1, wherein: In step S5, the kneading speed is 500-1000 rpm, and the kneading temperature is 60-80°C.

7. A device for mixing powders, characterized in that: include: A stirring tank, wherein the mixed powder and the auxiliary liquid are contained in the stirring tank, a discharge port is opened at the lower left end of the stirring tank, and the outer wall of the stirring tank is covered with a cooling jacket; A stirring device, comprising a motor and a paddle, wherein the motor is mounted on the hatch of the stirring tank and connected to the paddle in the stirring tank via a connecting shaft; A cooling device, comprising a cooling system and a steam condenser disposed in the cooling system, wherein the steam condenser is connected to the stirring tank via a steam recovery pipe; A vacuum pumping device is installed on the side of the cooling device and is connected to the cooling system.

8. The powder mixing device according to claim 1, characterized in that: A thermometer is installed in the stirring tank.

9. The powder mixing device according to claim 1, characterized in that: A hatch lifting device is installed on the side of the mixing tank.

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