Nanovoid Formation and Annihilation in Gallium Nanodroplets under Lithiation–Delithiation Cycling

The
irreversible chemomechanical degradation is a critical issue
in the development of high-capacity electrode materials for the next-generation
lithium (Li)-ion batteries. Here we report the self-healing behavior
of gallium nanodroplets (GaNDs) under electrochemical cycling at room
temperature, observed with in situ transmission electron
microscopy (TEM). During lithiation, the GaNDs underwent a liquid-to-solid
phase transition, forming a crystalline phase (LixGa) with ∼160% volume expansion. Owing to the uneven
Li flow during lithiation, the fully lithiated GaNDs exhibited highly
distorted morphologies. Upon delithiation, the reverse phase transition
occurred, accompanied with the nucleation and growth of a nanosized
void. After the GaNDs were fully delithiated, the nanovoid gradually
annihilated. Our analysis, along with phase field modeling and experimental
measurements of the void growth and annihilation, provides mechanistic
insights into the void formation and annihilation mechanism. The GaNDs
may function as an effective healing agent in durable composite electrodes
for high-performance Li-ion batteries, wherein active components,
such as Si, are susceptible to fracture.