Spinel-type bimetal sulfides derived from Prussian blue analogues as efficient polysulfides mediators for lithium−sulfur batteries

More and more attentions have been attracted by lithium-sulfur batteries (Li-S), owing to the high energy density for the increasingly advanced energy storage system. While the poor cycling stability, due to the inherent polysulfide shuttle, seriously hampered their practical application. Recently, some polar hosts, like single metal oxides and sulfides, have been employed as hosts to interact with polysulfide intermediates. However, due to the inherent poor electrical conductivity of these polar hosts, a relatively low specific capacity is obtained. Herein, a spinel-type bimetal sulfide NiCo₂S₄ through a Prussian blue analogue derived methodology is reported as the novel host of polysulfide, which enables high-performance sulfur cathode with high Coulombic efficiency and low capacity decay. Notably, the Li-S battery with NiCo₂S₄-S composites cathode still maintains a capacity of 667 mAh/g at 0.5 C after 300 cycles, and 399 mAh/g at 1 C after 300 cycles. Even after 300 cycles at the current density of 0.5 C, the capacity decays by 0.138% per cycle at high sulfur loading about 3 mg/cm². And the capacity decays by 0.026% per cycle after 1000 cycles, when the rate is 1 C. More importantly, the cathode of NiCo₂S₄-S composite shows the outstanding discharge capacity, owing to its good conduction, high catalytic ability and the strong confinement of polysulfides.