Ultrasonic Homogenizer: An Efficient Tool for Defoaming Battery Slurry

Ultrasonic waves: An effective tool for defoaming battery slurries

During the battery production process, the quality of the battery slurry plays a critical role in battery performance. However, bubbles often enter the slurry, acting like "little bombs" hidden within the battery, negatively impacting its performance and quality. For example, the presence of bubbles can cause holes and uneven thickness in the battery electrode during coating, further impacting the battery's charge-discharge performance, cycle life, and safety. Therefore, efficiently removing bubbles from battery slurries has become a crucial step in the battery production process. Ultrasonic technology, as an advanced defoaming method, is gradually gaining prominence in the battery industry.

I. Sources and Hazards of Bubbles in Battery Slurry

  (I) Sources of Bubbles

During the preparation of battery slurry, bubbles can be introduced at multiple stages. First, the raw materials themselves may carry gases. For example, some powdered active materials may absorb a certain amount of air during storage or transportation. Second, stirring is an essential step in battery slurry preparation. During high-speed stirring, air can be drawn into the slurry, forming bubbles. Furthermore, bubbles can also be introduced during the transportation and transfer of the slurry due to contact with air or impact.

  (II) Hazards of Bubbles

1. Impact on Electrode Coating Quality: When a slurry containing bubbles is applied, the bubbles can form cavities or depressions on the electrode surface, resulting in uneven electrode thickness. This not only affects the battery's appearance but, more importantly, its electrochemical performance. For example, during charge and discharge, uneven electrode thickness leads to uneven current distribution, which can easily cause localized overheating and reduce the battery's cycle life.

2. Reduced Battery Performance: Bubbles occupy the available space in the slurry, reducing the actual content of active materials and thus lowering the battery's energy density. Furthermore, bubbles can affect ion transport within the battery, increasing the battery's internal resistance and reducing its charge and discharge efficiency. In extreme cases, bubbles can cause internal short circuits in the battery, leading to safety accidents.

II. Principles of Ultrasonic Defoaming

  (I) Cavitation

Ultrasound, a sound wave with a frequency above 20kHz, produces cavitation when applied to battery slurry. During the negative pressure half-cycle of the ultrasonic wave, tiny bubbles in the liquid rapidly expand; during the positive pressure half-cycle, the bubbles shrink dramatically until they burst. This process, when the bubbles burst, generates a powerful impact force and micro-jets, with pressures reaching hundreds of atmospheres and temperatures reaching thousands of degrees Celsius. This localized high temperature and high pressure environment effectively destabilizes the bubbles in the slurry, causing them to burst and re-integrate with the slurry, thereby achieving the desired defoaming effect.

  (2) Resonance Effect

In addition to cavitation, ultrasound can also resonate with bubbles in the slurry. Each bubble has its own natural frequency. When the frequency of ultrasound approaches or equals the natural frequency of a bubble, it triggers resonance. In this resonant state, the amplitude of the bubble's vibration increases dramatically, making it more likely to burst. This resonance effect can specifically eliminate bubbles of a specific size, improving defoaming efficiency and accuracy.

III. Advantages of Ultrasonic Defoaming

    (1) High Efficiency and Speed

Compared to traditional defoaming methods, such as natural static defoaming or mechanical agitation, ultrasonic defoaming offers significant speed advantages. Natural static defoaming often takes a long time and is ineffective in removing tiny bubbles. While mechanical agitation can accelerate the removal of bubbles to a certain extent, it can easily introduce new bubbles and has limited defoaming effectiveness for some highly viscous slurries. Ultrasonic waves, on the other hand, can generate and rupture a large number of cavitation bubbles in a short period of time, quickly and effectively eliminating bubbles in the slurry. This significantly shortens defoaming time and improves production efficiency.

    (2) Deep Defoaming

The cavitation and resonance effects of ultrasonic waves penetrate deep into the slurry, affecting both tiny bubbles and those hidden deep within. They can remove bubbles adsorbed on the surface of solid particles and coalesce tiny bubbles dispersed in the slurry into larger bubbles for expulsion, achieving deep defoaming and effectively improving the quality and uniformity of the slurry. 

    (3) Minimal Impact on Slurry Properties

Ultrasonic defoaming is a physical defoaming method that does not require the addition of any chemical defoaming agents. Therefore, it does not alter the chemical composition or physical properties of the battery slurry. This is particularly important for battery production, where slurry quality is extremely demanding, as it ensures that battery performance is not affected by the defoaming process. It also avoids the potential environmental pollution caused by residual chemical defoaming agents.

    (4) Easy Integration and Automated Control

Ultrasonic equipment is small and compact, making it easy to integrate into existing battery slurry production lines. When combined with an automated control system, ultrasonic operating parameters such as power and frequency can be adjusted in real time based on slurry flow rate, concentration, and other parameters. This enables automated control of the defoaming process and improves the stability and consistency of the production process.

IV. Examples of Ultrasonic Defoaming Applications in Battery Production

(1) Lithium Battery Production

Ultrasonic defoaming technology is widely used in the preparation of both positive and negative electrode slurries for lithium batteries. For example, after adopting ultrasonic defoaming equipment, a lithium battery manufacturer reduced porosity defects during electrode coating by over 80%, increased the battery's initial charge and discharge efficiency by 5%, and significantly extended its cycle life. The ultrasonic defoaming equipment used by this company is installed at the bottom of the mixing tank. A specialized transducer transmits ultrasonic energy to the slurry, achieving efficient defoaming without affecting the existing production process.

(2) Fuel Cell Production

Ultrasonic defoaming also plays a vital role in the preparation of fuel cell electrode slurries. Because fuel cells place extremely high demands on electrode performance, bubbles in the slurry must be completely removed. A fuel cell R&D company uses an ultrasonic cleaner to defoam the electrode slurry and also incorporates a sieving system to filter the slurry. Under the vibration of ultrasound, the screener can more effectively filter out unevenly dispersed particles, and at the same time use sound waves to burst bubbles, achieving the dual effects of defoaming and filtration, greatly improving the quality and performance of fuel cell electrodes.