What Is The Principle of Cathode/Anode Sheet Drying?

1. Three Methods of Sheet Drying

1.1 Far-Infrared Radiation Drying  

Uses far-infrared emitting elements to radiate heat energy onto the surface of the material to be dried, causing the liquid to evaporate and vaporize for drying;

1.2 Double-Sided Airflow Floating Drying  

Floating drying involves setting specially designed air nozzles on both sides of the drying foil, delivering high-speed airflow. Due to the wall effect of the air movement, the airflow acts vertically on the drying foil, and under the action of the airflow, the drying sheet remains in a floating state.

1.3 Circulating Hot Air Impact Drying  

A high-efficiency drying technology developed based on the principles of air jet fluid dynamics. Drying air is jetted onto the surface of the material through specially designed air nozzles at high speed. The stagnant air layer that inhibits drying on the surface is disrupted by the impact of the airflow, greatly improving the drying efficiency.

The characteristics of the three drying methods:

2. Basic Principles of Drying

Drying is the process of using heat to vaporize water or other solvents and removing the resulting vapor to eliminate moisture from solid materials.

2.1 Conditions for the Drying Process:

1. Pw > P, the driving force causes the moisture in the material to vaporize;

2. Pw = P, pressure is balanced, and the drying process stops;

3. Pw < P, the driving force causes the material to absorb moisture.

2.2 Kinetics of Drying:

The drying process is divided into the preheating and warming stage AB, the constant rate drying stage BC, and the falling rate drying stage CDE.

Drying Process:

1.  Preheating and Heating Stage (AB): The material is heated and its temperature increases.

2.  Constant Rate Drying Stage (BC): The heat from the steam is absorbed by the material. The vapor pressure of the moisture exceeds that of the hot air, initiating moisture vaporization. The evaporation rate and the diffusion rate are nearly equal, resulting in a stable, constant drying rate. At this stage, moisture in the wet film evaporates rapidly, causing the coating to begin shrinking and deforming. Internal stress gradually increases. If this stress exceeds the adhesive force between material particles, cracking may occur.

3.  First Falling Rate Stage (CD): The internal moisture diffusion rate within the material becomes lower than the surface moisture evaporation rate. A "dry zone" forms in the material, leading to a decrease in the drying rate. The internal stress begins to stabilize.

4.  Second Falling Rate Stage (DE): The moisture evaporation front gradually moves into the interior of the material. Increased internal resistance causes a further decrease in the drying rate.

Schematic diagram of the electrode sheet drying process: The components of the lithium battery electrode slurry are evenly distributed, and then solvent evaporation induces a reduction in the thickness of the wet coating. The particles gradually move closer to each other until the densest packing state is formed, and the coating shrinkage stops. As the moisture vaporization front advances into the pore structure, a porous dry electrode coating is eventually formed.