Strategic Design of a Functional Separator with Dual-Acting Si/SiO_x Nanocomposite for Dendrite-Free Li-Metal...

The development of functional separators that prevent the formation and growth of Li-metal dendrites in Li-metal batteries (LMBs) follows two main trends: introducing functional materials capable of (1) controlling Li⁺ transport or (2) reacting with Li metal. However, which of the two functions introduced into the separator more effectively suppresses the formation and growth of Li dendrites remains unclear. To unveil the distinct role of these two functions in functional separators, three different types of silicon-based functional materials with distinct properties were utilized in the separator; namely, silicon nanoparticles that explosively react with Li metal, silicon dioxide nanoparticles that react slightly with Li metal and are capable of changing the solvation structure of Li, and silicon dioxide microparticles that only change the solvation structure of Li. Controlled experiments confirm a strong correlation between the polar properties of the coating materials and the initial morphology of the Li plating, whereas the reactivity of the coating materials with Li metal predominantly influences the growth of Li dendrites. Consequently, the formation and growth of Li dendrites can be effectively controlled when both functions of the functional materials coated on the separator are sustainably coordinated without loss of the individual functions. Inspired these findings, a dual-acting functional separator for suppressing the formation and growth of Li dendrites was developed using 10 nm Si-nanodot-embedded amorphous SiO₂ nanoparticles. The harmonious coordination of the Si nanoparticles and SiO₂ matrix constituting SiO_x afforded improved electrochemical performance of Li||Li and Li||Cu half-cells and a Li||NCM811 full cell.