(Invited) Dendrite Formation in Lithium Electrodeposition – Insights from Experiments and Modeling

Abstract

High-energy density batteries are essential for powering future electric vehicles and electric aircrafts. The Li-metal anode offers the highest theoretical specific energy among practically available anode materials; however, a major hurdle in the progress towards rechargeable Li-metal batteries is the dendritic electrodeposition of Li metal during the battery charging process. The physicochemical mechanisms behind Li dendrite formation have been a topic of rich and fervent research, but many questions remain presently unanswered. Among these, a key question of significance to battery charging is: at what time instant is Li dendritic growth initiated? In the present talk, this question will be addressed through a combination of experiments and modeling. Chronopotentiometry during galvanostatic Li electrodeposition coupled with in situ optical microscopy reveals that the first emergence of Li dendrites corresponds to the time instant when the surface overpotential reaches a maximum.1 Electrochemical impedance spectroscopy shows that the increase in the surface overpotential preceding this maximum is due to gradual growth of the solid electrolyte interphase (SEI). This SEI layer growth induces Li+ concentration depletion at the electrode-SEI interface, promoting amplification of surface asperities and thus dendrites that rupture the SEI. A transport model incorporating Li+ diffusion across a growing SEI layer is developed, and shown to predict Li dendrite onset times that are in good agreement with experimental observations over a wide range of current densities, temperature, and initial SEI thicknesses.2 A key conclusion of our work is that liquid-phase mass transport limitations, often characterized by the Sand’s equation, do not reliably predict the onset of Li dendrites.3 Rather, transport characteristics and associated instabilities within solid-phase surface films on Li are predominantly responsible for dendrite formation. Our work provides clues for how dendrite formation could be arrested for enabling rechargeable Li-metal anodes for use in next-generation batteries.