Mechanochemical optimization of ZIF-8/Carbon/S8 composites for lithium-sulfur batteries positive electrodes

Abstract

• Mechanochemical approaches for the preparation of ZIF-8 carbon composites. • Mechanochemical preparation of ZIF-8-related structures by Zn 2+ replacement. • Different approaches for incorporation of conductive carbon in all ZIF structures. • ZIF-8/carbon/S 8 composite presented initial capacities of 772 mA h g −1 . • Lithium Polysulfides are better incorporated by the ZIF-8 carbon material. The application of lithium-sulfur (Li-S) batteries is still limited by their rapid capacity fading. The pulverization of the sulfur positive electrode after the lithiation and the consequence dissolution of long chain polysulfides in organic solvents lead to the shuttle effect. To address these issues, here we report the mechanochemical preparation of ZIF-8 ( Zeolitic Imidazole Framework-8 )-based composites as sulfur hosts for positive electrodes in Li-S batteries. We studied different methods for the incorporation of conductive carbon. Also, the replacement of Zn 2+ metal centers by other bivalent metals (Cu 2+ , Co 2+ and Ni 2+ ), enabled the preparation of other ZIF-8-based materials. The positive electrode ZIF-8/C/S 8 showed initial discharges of 772 mA h g −1 while the pristine one, ZIF-8/S 8 , displayed 502 mA h g −1 . The enhanced performance of 54% for ZIF-8/C/S 8 indicates that the direct mechanochemical synthesis of ZIF-8 with conductive carbon is beneficial at initials charge/discharge process in comparison to traditional slurry preparation (ZIF-8/S 8 ). Also, the Li 2 S 6 absorption tests shows 87% of discoloration with ZIF-8/C/S 8 , confirming the better polysulfides absorption.