Nano-compacted Li2S/Graphene Composite Cathode for High-Energy Lithium-Sulfur Batteries

Abstract

A mixture of graphene and Li2S is pelletized by a volume reduction of 220% to synthesize a high energy density cathode for lithium-sulfur (Li-S) batteries. The compacted graphene/Li2S composite cathode, in addition to providing robust electrical pathways, drives Li2S metastable particles to metastable states (high-pressure polymorphs with a highly deformed mechanical state), triggering a spontaneous conversion of Li2S to S-8 in the first charging process. This direct conversion resolves the long-standing problem of excess polysulfide formation during Li2S activation. Moreover, graphene sheets, tightly encapsulating the Li2S particles, effectively confine the active material in subsequent cycles to ensure unprecedented cycling stability at a high loading density for the Li-S battery. Here we show a major breakthrough in Li-S battery technology, providing the high energy density promised by the proposed technology while ensuring the required battery lifetime. Furthermore, successful operation of a pouch-type cell employing the pelletized graphene/Li2S composite cathode with a high loading level clearly demonstrates the convenience of scaling up the proposed pelletization of Li2S or S cathodes to a large-format Li-S battery.