In Situ TEM Study of Self-healing Gallium Nanodroplets under Electrochemical Cycling
Wentao Liang (Penn State University), Liang Hong (Penn State University), Hui Yang (Penn State University), Long-Qing Chen (Penn State University), Jianyu Huang (), Ting Zhu (), Sulin Zhang (Penn State University)
Lithium ion batteries: When Chemistry meets Mechanics
Mon 10:45 - 12:15
Salomon 003
Irreversible chemo-mechanical degradation of high-capacity electrode materials remains a critical issue in the development of the next-generation lithium (Li)-ion batteries. Here we report the self-healing behavior of gallium nanodroplets (GaNDs) under electrochemical cycling using in situ transmission electron microscopy (TEM). During lithiation, the GaNDs in the amorphous phase underwent liquid-to-solid phase transition, forming a crystalline phase (LixGa) with 160% volume expansion. The fully lithiated GaNDs exhibited highly distorted morphologies, owing to the uneven Li flow induced by the constraining effects to the GaND expansion during lithiation. Upon delithiation, the reverse phase transition occurred, and electrochemical extraction of Li led to the nucleation and growth of a nanovoid inside the GaNDs. After the GaNDs were fully delithiated, the nanovoid gradually annihilated, exhibiting a self-healing behavior. Our kinetics analysis shows that the void growth obeys a logarithmic time law while the annihilation follows a cubic function. We developed a phase field model with which we revealed that the nucleation and growth morphologies of the nanovoid depend critically on the normality of the Li concentration gradient to the GaND surface. The self-healing capability of GaNDs opens up a new pathway for mitigating the chemo-mechanical degradation of high-capacity electrodes.