PNNL

Abstract

Electrolyte regulation for sulfurized polyacrylonitrile (SPAN) cathode in lithium (Li) metal batteries is widely reported but the original formation and protection mechanisms of the cathode/electrolyte interphase (CEI) layer formed on SPAN have been unclear for a long time. Carbonate-based and ether-based electrolytes are two typical electrolyte systems which have been demonstrated to be favorable by SPAN and Li metal. In this work, an advanced ether-based electrolyte containing LiFSI, ether and partially fluorinated ether and a conventional LiPF6/carbonate electrolyte are employed to investigate the origin of the CEI growth on SPAN surface through computational simulations and experimental characterizations. The partially fluorinated ether is revealed to not only act as a protective shield to prevent the polysulfides dissolution by ether solvent but also be a booster to promote the formation of a protective and conductive CEI layer pinning into the SPAN surface region. Consequently, the Li||SPAN cells with the ether-based electrolyte demonstrate a high capacity retention of 86.9 % after 400 cycles with a high sulfur loading of ~5.0 mg cm-2 in the SPAN cathode. The deep understanding of CEI formation origins in SPAN provides inspiring guidance for the rational design of advanced electrolytes for Li||SPAN battery and paves the way to future high energy density Li-sulfur applications.