Polyhedral Oligomeric Silsesquioxane Modified Polyolefin Separator for Advanced Lithium–Metal Batteries

Poor rate capability, unstable cycling performance, and dendrite-induced short circuits are knotty issues that hinder the practical application of rechargeable lithium metal batteries. Separators with good electrolyte wettability and heat resistance are an attractive alternative to improve the electrochemistry performance while preventing dendrite growth by stabilizing the solid electrolyte interphase. Here, we report a multifunctional separator that addresses the above issues through a simple and scalable surface modification strategy by deposition of polyhedral oligomeric silsesquioxane (POSS) nanoparticle combined with polydopamine (PDA)/polyethylenimine (PEI) on the traditional polyethylene (PE) separator. Benefiting from the abundant O, N-containing groups, and Si–O groups, the composite separator can redistribute the Li+ in the electrolyte for rapid diffusion and uniform transfer of Li+, guaranteeing the long-term stability of the Li stripping/plating process as well as preventing the dendrite growth. Meanwhile, these functional groups can act as polar sites to improve the wettability of the electrolyte. Consequently, the assembled LiFePO4/Li cells with POSS–PDA-PEI/PE multilayer separator show good electrochemical performance, including high ionic conductivity (0.77 mS/cm), high lithium-ion transference number (0.42), and the long-term cycling process with lower capacity decay (0.018% at 1 C after 1000 cycles and 0.034% at 4 C after 500 cycles). This work demonstrates the potential of composite separators for high-performance lithium metal batteries by achieving a stable electrochemical interface between the anode and cathode.