Bidirectionally catalytic polysulfide conversion by high-conductive metal carbides for lithium-sulfur batteries

Abstract

Utilizing catalysts to accelerate the redox kinetics of lithium polysulfides (LiPSs) is a promising strategy to alleviate the shuttle effect of lithium–sulfur (Li–S) batteries. Nevertheless, most of the reported catalysts are only effective for LiPSs reduction, resulting in the devitalization of catalysts over extended cycles as a consequence of the continuous accumulation of Li2S passivation layer. The situation gets even worse when employing mono-directional catalyst with poor electron conductivity because the charge transfer for the decomposition of solid Li2S is severely hampered. Herein, a high-conductive and dual-directional catalyst Co3C decorated on porous nitrogen-doped graphene-like structure and carbon nanotube (Co3C@PNGr-CNT) is fabricated as sulfur host, which not only promotes the precipitation of Li2S from LiPSs during discharge but also facilitates the decomposition of Li2S during subsequent charge, as evidenced by the reduced activation energies for both reduction and oxidation processes. Furthermore, the long-term catalytic stability of Co3C is corroborated by the reversible evolution of Co–C bond length over extended cycles as observed from X-ray absorption fine structure results. As a consequence, the fabricated Co3C@PNGr-CNT/S cathode delivers a low capacity decay of 0.043% per cycle over 1000 cycles at 2C. Even at high sulfur loading (15.6 mg cm−2) and low electrolyte/sulfur (E/S) ratio (∼8 μL mg−1) conditions, the battery still delivers an outstanding areal capacity of 11.05 mAh cm−2 after 40 cycles. This work provides a rational strategy for designing high-efficient bidirectional catalyst with single component for high-performance Li-S batteries.