Nucleation and Early Stage Growth of Li Electrodeposits

The morphologies that metal electrodeposits form during the earliest stages of electrodeposition are known to play a critical role in the recharge of electrochemical cells that use metals as anodes. 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 (SEM) 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 in regulating  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.