Polysulfide-Breathing/Dual-Conductive, Heterolayered Battery Separator Membranes Based on 0D/1D Mingled Nanomaterial Composite Mats

Abstract

Facile/sustainable utilization of sulfur active materials is an ultimate challenge in high-performance lithium sulfur (Li-S) batteries. Here, as a membrane-driven approach to address this issue, we demonstrate a new class of polysulfide-breathing (capable of reversibly adsorbing and desorbing polysulfides)/dual (electron and ion) conductive, heterolayered battery separator membranes (denoted as "MEC-AA separators") based on 0D (nanoparticles)/1D (nanofibers) composite mats. The MEC-AA separator is fabricated through an in-series, concurrent electrospraying/electrospinning process. The top layer of the MEC-AA separator comprises close packed mesoporous MCM-41 nanoparticles spatially besieged by multiwalled carbon nanotubes (MWNT) wrapped poly (ether imide) (PEI) nanofibers. The MCM-41 in the top layer shows reversible adsorption/desorption of polysulfides, and the MWNT-wrapped PEI nanofibers act as a dual-conductive upper current collector. Preferential deposition of the MWNTs along the PEI nanofibers and dispersion state of the separator components are elucidated theoretically using computational methods. The support layer, which consists of densely packed Al2O3 nanopartides and polyacrylonitrile nanofibers, serves as a mechanically/thermally stable and polysulfide-capturing porous membrane. The unique structure and multifunctionality of the MEC-AA separator allow for substantial improvements in redox reaction kinetics and cycling performance of Li-S cells far beyond those achievable with conventional polyolefin separators. The heterolayered nanomat-based membrane strategy opens a new route toward electrochemically active/permselective advanced battery separators.