Interaction mechanism between MOF derived cobalt/rGO composite and sulfur for long cycle life of lithium–sulfur batteries

Abstract

Within the ever-growing family of lithium batteries, lithium–sulfur batteries (LSB) have gained significant commercial concern owing to the impressive specific theoretical capacity of 1675 mAhg⁻¹. Despite possessing a higher theoretical specific capacity, lithium-sulfur batteries (LSBs) face practical challenges due to the mobility of dissolved polysulfide intermediates, shuttle effect and the insulating properties of sulfur. These factors result in limited utilization of active material and rapid capacity deterioration. To minimize these problems, we designed a sponge cobalt wrapped in reduced graphene oxide (rGO) cathode material to enable effective polysulfide immobilization. The sponge cobalt nanoparticles from the ZIF 67 metal organic framework wrapped in rGO nanosheets increase the amount of space inside the carbon sponge; thus, has the significance for containing large amount of sulfur. The high affinity of cobalt for lithium polysulfide enabled robust lithium polysulfide adsorption against shuttling effects. The bonding between the cobalt and carbon functional groups captures lithium polysulfides on the composite surface, preventing their dissolution in the electrolyte. The cohabitation of sulfur and cobalt on rGO accelerated electron transfer rate for the transformation of sulfur, leading to efficient suppression of shuttle effect and steady sulfur electrochemistry. The sponge sulfur-infiltrated cobalt nanoparticles into rGO sheets exhibit a discharge capacity of 1176 mAhg⁻¹ at 200 mAg⁻¹ current density with cycling stability and retention capacity rate of 91 % for more than 140 cycles.