Meaning
Internal structural defects appearing as microscopic cavities within electrode coatings or solid electrolyte layers influence the density and ionic transport of a battery cell. Micro-voids often form during the solvent evaporation phase of the slurry casting process or as a result of incomplete particle packing during calendering. These empty spaces increase the effective path length for lithium ions and can act as sites for electrolyte decomposition.
Reduced contact area between particles also increases the internal resistance of the electrode.
Formation Mechanism
Evaporation rates during the drying of the electrode slurry determine the size and distribution of these pores. If the temperature is too high, the solvent escapes rapidly and leaves behind micro-voids that weaken the mechanical bond. This phenomenon is a primary concern for high-loading electrodes.
Impedance Impact
Electrical and ionic resistance within the cell is directly affected by the presence of these internal gaps. Because micro-voids do not contain active material or conductive additives, they act as insulating barriers to electron flow. This local increase in impedance causes non-uniform current distribution and can lead to the formation of hot spots during high-rate discharge.
The resulting thermal stress accelerates the aging of the surrounding material.
Coating Optimization
Adjusting the binder content or the calendering pressure allows manufacturers to minimize the volume of these defects. A successful coating process balances the need for porosity to allow electrolyte wetting with the need for density to ensure high energy storage. This optimization is necessary for achieving long cycle life.
