Meaning
Localized accumulation and solid crystallization of electrolyte salts within the porous network of an electrode block ionic transport pathways. When extreme concentration gradients arise, spatial salt precipitation occurs at the electrode boundaries where the solubility limit is exceeded. This localized blockage halts the flow of ions and causes a sharp rise in internal resistance.
Precipitation Driver
High current densities combined with low operating temperatures drive this localized phase transition. At negative temperatures, the solubility of standard salts like lithium hexafluorophosphate drops dramatically. Reduced diffusion rates simultaneously slow the dispersion of ions, causing the salt concentration to exceed critical limits near the current collectors.
Pore Occlusion
Structural examination of aged cells shows that this precipitation is unevenly distributed across the electrode thickness. Solid crystals accumulate primarily in the narrowest pores and near the separator interface, where the concentration gradient is most severe. This physical obstruction permanently decreases the active surface area of the electrode.
Performance Failure
Sourcing specifications for grid storage batteries must account for this phenomenon, especially when cells are designed for cold climates or high power demands. Purchasing contracts often specify electrolytes with specialized co-solvents that suppress crystallization and maintain high salt solubility. This preventative measure ensures that the batteries can operate at high discharge rates without suffering from sudden capacity loss or irreversible pore blockages during winter operation.
