Dendrite-free lithium deposition with self-aligned nanorod structure

Suppressing lithium (Li) dendrite growth is one of the most critical challenges for the development of Li metal batteries. Here, we report for the first time the growth of dendrite-free lithium films with a self-aligned and highly compacted nanorod structure when the film was deposited in the electrolyte consisting of 1.0 M LiPF₆ in propylene carbonate with 0.05 M CsPF₆ as an additive. Evolution of both the surface and the cross-sectional morphologies of the Li films during repeated Li deposition/stripping processes were systematically investigated. It is found that the formation of the compact Li nanorod structure is preceded by a solid electrolyte interphase (SEI) layer formed on the surface of the substrate. Electrochemical analysis indicates that an initial reduction process occurred at ∼2.05 V vs Li/Li⁺ before Li deposition is responsible for the formation of the initial SEI, while the X-ray photoelectron spectroscopy indicates that the presence of CsPF₆ additive can largely enhance the formation of LiF in this initial SEI. Hence, the smooth Li deposition in Cs⁺-containing electrolyte is the result of a synergistic effect of Cs⁺ additive and preformed SEI layer. A fundamental understanding on the composition, internal structure, and evolution of Li metal films may lead to new approaches to stabilize the long-term cycling stability of Li metal and other metal anodes for energy storage applications.