Mg-based inorganic nanofibers constructing fast and multi-dimensional ion conductive pathways for all-solid-state lithium metal batteries

Abstract

Solid-state electrolytes (SSEs), which replace flammable and toxic liquid electrolytes, have attracted widely attention. However, there exist still some challenges in actual application such as poor interfacial compatibility and slow ionic migration. In this study, MgO nanofibers and MgF2 nanofibers were prepared via the electro-blow spinning and high-temperature calcination methods, and were applied to all-solid-state lithium metal batteries for the first time. The organic-inorganic composite SSEs exhibited continuous conduction paths based on the virtue of the nanofibers with high length-to-diameter ratio, which were designed and prepared by mixing prepared fillers into the poly(ethylene oxide) (PEO)/ lithium bis(trifluoromethane) sulfonilimide (LiTFSI) system. The effect of filler with different morphologies, doping ratios and component on ionic conductivity, electrochemical stability and cycle performance were explored under two kinds of [EO]/[Li+] ratios and ambient temperatures. The ionic conductivities of electrolytes containing MgO and MgF2 nanofibers can reach up to 1.19 × 10−4 and 1.39 × 10−4 S cm−1 at 30 °C, respectively. They were attributed to specific ionic conductive enhancement at the organic-inorganic interface, reduced crystallinity and Lewis acid interaction, which can effectively promote the dissociation of the lithium salts. Especially MgF2 nanofiber, combining low electronic conductance, excellent electrochemical stability and outstanding inhibition for lithium dendrites of fluorides, endowed the battery with an initial specific capacity of 140.6 mAh g−1 and capacity decay rate per cycle of 0.055% after 500 cycles at 50 °C. The work can provide an idea to design SSE with fast and multi-dimensional Li conductive paths and excellent interfacial compatibility.