Electrolyte Confinement Alters Lithium Electrodeposition

The metastability of lithium electrodeposition continues to be a scientific mystery. Local ionic depletion has been conventionally argued to be a root cause for nonlinear morphological manifestations. Given the bulk nature of electrolyte transport limitation, it should be absent for very small interelectrode separations; however, even under such conditions, sustained electrodeposition is not observed. We find that the passivating film formed due to lithium’s high reactivity alters the surface energies and in turn deposition preference for fresh lithium. This asymmetry in deposition preference leads to nonuniform surface structure growth and traps the electrolyte layer. Such electrolyte confinement causes polarization, even at subcritical currents. The existence of confined electrolyte and associated electrochemical complexations is proved through temperature-controlled electrodeposition experiments.