Regulating Li ions transportation and deposition with polydopamine/polyethyleneimine functional separator for superior Li metal battery

Multifunctional modified separators have the potential to effectively regulate Li ion deposition, suppress the growth of dendrite and improve the safety of lithium metal batteries (LMBs). Here, we designed a separator, constructed by co-deposition of polydopamine (PDA) and polyethyleneimine (PEI) on PP separator. Due to the introduction of polar functional groups such as amine groups, PDA/PEI-3 modified separator exhibits better electrolyte wettability, higher Li ion migration number (0.9), lower energy barrier and faster ion transfer kinetics. Electrochemical tests prove that PDA/PEI-3 modified separator has achieved better cycling stability at different current density in Li//Li symmetric cells and higher CE in Li//Cu cells. Meanwhile, the Li/LFP full cells show more excellent rate performance and long cycle performance (80%). SEM and XPS also prove that modified separator has achieved homogenized Li ions flux and more uniform LiF-rich SEI layer. This work provides a simple and effective strategy for functional separator to protect Li metal anode and improve safety performance of LMBs.