Meaning
Physical phenomenon where the microscopic voids in a battery separator or electrode close up due to thermal, mechanical, or chemical stress. This loss of porosity restricts or completely blocks the movement of ions, which significantly increases internal resistance and can lead to the termination of cell function. Pore collapse is often a deliberate safety feature in shutdown separators but can also be a degradation mode if it occurs prematurely during cycling.
The process is typically irreversible once the polymer or active material structure has been compressed or melted.
Safety Mechanism
Thermal shutdown separators are engineered to trigger this state when the cell reaches a critical temperature. During a controlled pore collapse, the polyolefin material melts slightly and fills the gaps that previously held the electrolyte. This intervention stops the current flow and prevents the cell from entering a state of thermal runaway by cutting off the electrochemical energy source.
Mechanical Deformation
Excessive stack pressure or external impact can crush the delicate structure of the electrodes and the separator film. Mechanical pore collapse reduces the volume available for electrolyte wetting and slows down the diffusion of lithium ions. This leads to increased polarization and a reduction in the usable power of the battery pack.
Long Term Aging
Chemical byproducts from electrolyte decomposition can gradually accumulate and fill the open spaces within the electrode matrix. This form of pore collapse happens over hundreds of cycles as solid interphase layers grow too thick. The resulting loss of ion pathways contributes to the capacity fade and the rising impedance observed in older battery systems.
