Functional Separator Decorated with Polydopamine and Halloysite Nanotubes to Boost Li⁺ Transfer in Lithium Metal Batteries

Abstract Commercialization of lithium‐metal batteries is impeded by Li dendrites. Realizing a high Li⁺ transference number is an effective strategy to suppress the formation of Li dendrites by alleviating the Li⁺ concentration gradient at the Li metal surface. Accordingly, various materials that facilitate Li⁺ transfer have been investigated in separator engineering. Herein, we designed a functional separator incorporating halloysite nanotubes (HNTs) as a functional material and polydopamine (PDA) as a polymeric binder. PDA plays a significant role in improving electrolyte affinity as it renders the overall backbone of PE hydrophilic. Moreover, the PDA/HNTs/PE separator shows a high Li⁺ transference number (0.603) owing to the interactions of HNTs: 1) the electrostatic attraction between the negatively‐charged silicon layer and Li⁺, and 2) dipole‐dipole interactions between HNTs and electrolyte solvent molecules, which reduce the degree of Li⁺ solvation. Consequently, dendrite‐free Li deposition was observed with the PDA/HNTs/PE separator, improving the electrochemical performance of Li/Li symmetric cells and Li/LiFePO₄ full cells.