Nanoscale Polycyclosiloxane Interlayer for Enhanced Lithium Plating on Copper

The stabilization of the highly reactive Li metal/electrolyte interface is one of the critical challenges limiting the practical implementation of Li metal batteries. Specifically, “anode-free″ Li metal battery configurations offer unprecedented energy density but suffer from inhomogeneous and irreversible Li plating and stripping at the Cu/electrolyte interface. In this work, we employ initiated chemical vapor deposition (iCVD) to passivate Cu current collectors with a thin-film polymer, poly(1,3,5,7-tetravinyl-1,3,5,7-tetramethylcyclotetrasiloxane) (pV4D4). The electrochemical performances of pV4D4 coatings at 5, 25, and 147 nm thickness are characterized and their mechanistic role elucidated through surface analysis of the electrodeposited Li metal on each substrate. We observe two distinct Li plating mechanisms based on the thickness of the iCVD layer. At the 25 nm pV4D4-modified Cu substrate, we observe highly stable Li plating and stripping, with the pV4D4 serving as an artificial SEI that mitigates electrolyte decomposition and facilities a uniform flux of Li + to produce a dense Li deposit beneath the interlayer. The 147 nm pV4D4-modified Cu substrate offers improvement versus bare Cu and 5 nm pV4D4, through its functionality as a nucleation layer with Li depositing atop the interlayer. Overall, this work provides the first demonstration of pV4D4-enabled Li electrodeposition, paving the way for further opportunities of nanoscale polymeric coatings for controlling ion transport across electrochemical interfaces.