Co₄N Nanosheet Assembled Mesoporous Sphere as a Matrix for Ultrahigh Sulfur Content Lithium-Sulfur Batteries.

Abstract

High utilization and loading of sulfur in cathodes holds the key in the realization of Li-S batteries. We here synthesized a Co₄N mesoporous sphere, which was made up of nanosheets, via an easy and convenient method. This material presents high affinity, speedy trapping, and absorbing capacity for polysulfides and acts as a bifunctional catalysis for sulfur redox processes; therefore it is an ideal matrix for S active material. With such a mesoporous sphere used as a sulfur host in Li-S batteries, extraordinary electrochemistry performance has been achieved. With a sulfur content of 72.3 wt % in the composite, the Co₄N@S delivered a high specific discharge capacity of 1659 mAh g^-1 at 0.1 C, almost reaching its theoretic capacity. Also, the battery exhibited a large reversible capacity of about 1100 mAh g^-1 at 0.5 C and 1000 mAh g^-1 at 1 C after 100 cycles. At a high rate of 2 C and 5 C, after 300 cycles, the discharge capacity finally stabilized at 805 and 585 mAh g^-1. Even at a 94.88% sulfur content, the cathode can still deliver an extremely high specific discharge capacity of 1259 mAh g^-1 with good cycle performance.