Controlling hydroxyl content of reduced graphene oxide for superior cathode performance of lithium sulfur batteries

Abstract

Here, the hydroxyl content of reduced graphene oxide (rGO) is controlled by adjusting reduction time with l-ascorbic acid as reduction agent to study the effect on cathode performance of lithium sulfur batteries (LSBs). The results indicate that the hydroxyl content decreases from 35.8% to 17.9% with prolonging reduction time from 6 h to 48 h, and the C/O ratio increases. More importantly, it is demonstrated that the rGO with relatively low hydroxyl content within 36 h of reduction is more beneficial to enhance both the initial capacity and capacity retention as well as rate performance of LSBs, which is ascribed to the higher conductivity, stronger adsorption and relatively few reaction by-products with the decrease of hydroxyl content. However, when the reduction time is further prolonged to 48 h, the cathode performance deteriorates. As a result, rGO-36h/S electrode with the optimum hydroxyl content (19.2%) achieves an initial discharge capacity of 1340.9 mAh g−1, which still maintains 707.8 mAh g−1 over 100 cycles at 0.1C. This work may provide a guide for reducing GO when used as sulfur host material or matrix material of LSBs.