Well-dispersed amorphous Ta2O5 chemically grafted onto multi-walled carbon nanotubes for high-performance lithium sulfur battery

Abstract

Modification of commercial separators with conductive and active barrier layers towards soluble polysulfides is an effective way to combat the shuttle effect and improve the utilization rate of sulfur in lithium-sulfur (Li-S) batteries. Herein, well-dispersed amorphous Ta2O5 was chemically grafted onto oxidized multi-walled carbon nanotubes (CNT-O) under mild conditions by a one-pot solvent evaporation method. The prepared Ta2O5/CNT-O composite was used as a modified separator layer in a Li-S battery, which combined the advantages of the intertwined structure of conductive CNT-O and the chemisorption ability of Ta2O5. Cyclic voltammetry (CV) curves and X-ray photoelectron spectroscopy (XPS) verified the catalytic effect of Ta2O5 on the redox reactions during the discharge/charge processes and the strong chemical interactions between polysulfides and Ta2O5. Scanning electron microscopy (SEM) images of the modified separators after cycling revealed that the well-dispersed amorphous Ta2O5 could immobilize soluble polysulfides through chemical interactions and prevent aggregation of the insoluble products (Li2S2, LiS2 and S8) during the redox reactions, leading to a uniform redistribution of the sulfur species inside the modification layer, which could ensure the conductivity of the modification layer and high utilization rate of sulfur during long-term cycling processes. A Li-S cell prepared with Ta2O5/CNT-O modified separator exhibited a high initial specific capacity of 1230.7 mAh/g at a current density of 0.2 C and stable cycle performance with a decay rate of only 0.11% per cycle over 500 discharge/charge cycles.