Porous Cr2O3@C composite derived from metal organic framework in efficient semi-liquid lithium-sulfur battery

Abstract

A carbon composite including Cr2O3 (Cr2O3@C) and benefitting of a metal organic framework (MOF) precursor is herein synthesized, and originally employed in a semi-liquid lithium-sulfur cell using a catholyte solution formed by Li2S8 polysulfide, conducting lithium salt and film forming additive dissolved in diethylene glycol dimethyl ether (DEGDME). The adopted cell configuration may actually allow the porous structure of the MOF derivative to efficiently enable the lithium/sulfur electrochemical process. Thus, structure, chemical composition, morphology and porosity of the composite are investigated by X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, and N2 adsorption/desorption isotherms, respectively. The data reveal a mesoporous material consisting of aggregated nanometric particles (<100 nm) with relatively high BET surface area (170 m2 g−1), uniform element distribution, and a carbon content of about 13 wt%. Cyclic voltammetry of the Cr2O3@C in semi-liquid lithium sulfur cell using the catholyte solution shows a reversible reaction with fast kinetics and Li-diffusion coefficient ranging from about 3 × 10−8 cm2 s−1 at 2.4 V vs. Li+/Li, to 1 × 10−8 cm2 s−1 at 2 V vs. Li+/Li. Furthermore, electrochemical impedance spectroscopy reveals a very stable interphase with an impedance below 5 Ω after an activation process promoted by cycling. The semi-liquid Li/S cell operates with remarkable stability and efficiency approaching 100%, delivers a capacity ranging from 900 mAh g−1 at C/10 rate to 780 mAh g−1 at C/3 rate, and performs over 100 charge/discharge cycles with very modest capacity decay.