(334ax) Nucleation and Early Stage Growth of Lithium Electrodeposits

The morphologies metal electrodeposits adopt during the earliest stages of electrodeposition are known to play a critical role in the recharge of electrochemical cells that use metals as anodes. Lithium (Li) metal is among the most promising anode materials for high-energy and light-weight rechargeable batteries due to its extremely high theoretical specific capacity (3860 mAh g^−1), the lowest negative electrochemical potential (−3.040 V versus standard hydrogen electrode), and low density (0.534 g cm^−3). The propensity of Lithium Metal anode to form low-density mossy morphologies, loosely termed dendrites during the charging phase has impeded its practical application in Metal Batteries. The dendrites proliferate in the electrode space to short-circuit the battery producing thermal runaway, meanwhile lowering the coulombic efficiency (CE) and reversibility of the Lithium anode in electrolyte media. Studies dealing with understanding the nucleation and growth dynamics of reactive metals are cardinal to understand the origin of instabilities at early stages of electrodeposition that may subsequently lead to dendrites at a later stage. Here we report results from a combined theoretical and experimental study of the early-stage nucleation and growth of electrodeposited lithium at liquid-solid interfaces. The spatial characteristics of Lithium electrodeposits are studied via Scanning Electron Microscopy in tandem with Image analysis. Comparisons of Li nucleation and growth in multiple electrolytes provide a comprehensive picture of the initial nucleation and growth dynamics. We report that ion diffusion in the bulk electrolyte and through the Solid Electrolyte Interphase (SEI) formed spontaneously on the metal play equally important roles on Li nucleation and growth. We show further that the underlying physics dictating bulk and surface diffusion are similar across a range of electrolyte chemistries and measurement conditions and that fluorinated electrolytes produce a distinct flattening of Li electrodeposits at low rates. These observations are rationalized using X-ray Photoelectron Spectroscopy (XPS), Electrochemical Impedance Spectroscopy (EIS), and contact angle goniometry to probe the interfacial chemistry and dynamics. Our results show that high interfacial energy and high surface ion diffusivity are necessary for uniform Li plating.