Meaning
Chemical corrosion process involves the aggressive dissolution of metal oxides by an acidic byproduct formed from the breakdown of electrolyte salts. Trace moisture inside the cell reacts with lithium hexafluorophosphate to generate corrosive hydrofluoric acid attack targets. This mechanism governs the rate of manganese or nickel loss from cathode surfaces into the liquid solvent.
Metal Dissolution
Ions migrate from the crystal lattice into the electrolyte as the acidic molecules strip the protective surface layers away. Absence of a stable protective film allows the acid to penetrate deeper into the particle over time. Migration of these dissolved transition metals toward the anode causes the destruction of the solid electrolyte interface.
Surface Integrity
Erosion of the grain boundaries weakens the physical connection between primary particles within a cluster. When hydrofluoric acid attack progresses, the active surface area changes as secondary particles crumble into smaller fragments. Preventing this interaction requires meticulous drying of cell components and the inclusion of acid scavenging additives.
Storage Consequence
Elevated temperature increases the rate of salt decomposition and doubles the severity of the acidic interaction during long periods of inactivity. Cells kept at high states of charge are more prone to this degradation due to the sensitivity of delithiated oxides. Maintaining an anhydrous environment remains the standard practice for preventing this failure mode.
