Meaning
Directional migration of atomic-scale lattice vacancies through a solid crystal occurs in response to chemical, thermal or mechanical gradients. Vacancy flux governs the accumulation of microscopic voids at the interface between the lithium metal anode and the solid electrolyte during stripping. This transport behavior determines the onset of interfacial contact loss during high-rate discharge.
This transport process is highly sensitive to the operating temperature of the cell, which directly influences the diffusion coefficient of the vacancies within the metal lattice.
Solid-State Effect
Lithium ions are stripped from the metal anode during discharge, leaving behind vacant atomic sites at the contact interface. A high vacancy flux toward the interface can exceed the rate of metal plastic deformation, resulting in the coalescence of voids. These voids reduce the active contact area.
Current Concentration
Void formation concentrates the ion flux through the remaining contact points, leading to localized heating and high current densities. This localization increases the probability of dendrite growth during the subsequent charge cycle. Controlling this flux is crucial for preventing short circuits.
Mitigation Strategy
Applying external stack pressure or utilizing elevated temperatures increases the plastic flow of lithium metal, which offsets the vacancy accumulation. Incorporating transition metal alloys can also modify the diffusion dynamics of the lithium atoms. These measures preserve a stable interface over many cycles.
