Meaning
The retention of microscopic bubbles within highly viscous fluids during mixing or coating actions limits the density of battery active layers. Slurry preparation lines must avoid micro air void trapping to prevent structural gaps in the finished electrode coating. This phenomenon occurs when air becomes entrained in the carbon-active material mixture before the slurry is applied to the foil.
The parameter stops applying once the wet coating enters the dryer.
Fluid Dynamics
High-shear mixing forces air into the slurry when the fluid speed exceeds the capability of the agitator to maintain a smooth surface. During coating operations, micro air void trapping is exacerbated by high slurry viscosity and fast web speeds. The entrained air bubbles remain suspended due to the yield stress of the non-Newtonian fluid.
Vacuum degassing units operate during the transfer stage to remove these bubbles.
Quality Risk
Dry coating layers containing microscopic voids exhibit reduced mechanical adhesion and local electrical discontinuities. When micro air void trapping occurs, the resulting voids act as insulating pockets that block ionic transport. The adjacent regions experience elevated current densities, which can cause local overheating.
Electrode batches with excessive void volumes are rejected during automated inspection.
Prevention Method
Planetary centrifugal mixers operating under vacuum eliminate gas inclusions before the coating step. To reduce micro air void trapping, feed lines use inline degassing filters to capture residual microbubbles. Stable slurry formulation prevents foam stabilization.
