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.