A MOF-derived composite with multi-functional effects for high-performance Li–S batteries, especially its Co–N dual-catalyzing for S redox.

rapidly growing topic in the sulfur/carbon cathodes. [15][16][17][24][25][26][27][28][29][30] Although the porous structures of HCS favor the sulfur loading and electrolyte transport, the interaction between the nonpolar carbon shell and polar polysulfi de intermediates is not enough to suppress the dissolution of polysulfi de intermediates. More importantly, when used as the electrode materials, the large inner cavity of HCS usually results in the relatively low volumetric energy densities. Such an inherent drawback of HCS is undesirable for practical applications. [ 31,32 ] Following the development trend of the sulfur/carbon cathodes, the design of HCS should focus on the following aspects: (i) ultrahigh surface area to maximize the electrolyte permeation and interaction between HCS and sulfur/polysulfi des; (ii) heteroatom doping (e.g., nitrogen) to enhance the electrical conductivity of HCS and chemisorption between HCS and polysulfi de intermediates; (iii) shape optimization to improve conductive pathway and volumetric energy densities; (iv) facile and low-cost methodology to facilitate the practical applications.As a special class of hollow structures, bowl-like structure is an ideal methodology to increase the packing density of HCS. When used as the electrode materials, hollow carbon bowls (HCB) stacked within each other are also benefi cial to forming a favorable conductive pathway. However, there has been little success in using HCB to directly achieve high-performance energy storage components. [ 33,34 ] Recent research has indicated the unique biomedical applications of HCB. [35][36][37] Unfortunately, the reported HCB usually exhibit a low specifi c surface area (about 700-1000 m 2 g −1 ), which is much lower than HCS reported previously. [15][16][17][24][25][26][27][28][29] Since the utilization of chemical bonding between heteroatom doped carbon host and polysulfi de intermediates has been recently demonstrated as an effective way to further reduce the dissolution of polysulfi de intermediates, [38][39][40][41][42][43][44] the reported HCB with pristine carbon shell is diffi cult to meet the requirement for bonding polysulfi de intermediates. Therefore, the desirable HCB should not only inherit the advantages of HCS but also fulfi ll all above requirements for S/HCS cathodes. From the point of structure design, N-doped HCB (N-HCB) with high specifi c surface areas would open new opportunities for the sulfur/carbon cathodes. However, a new and effective methodology is the necessary prerequisite to the targeted N-HCB.Here, we present a facile route to synthesize N-doped HCS (N-HCS) and its N-HCB counterparts. Since the structure parameters of HCS can be precisely controlled by the prefabricated templates, hard-templating method is one of the most important routes to synthesize HCS. [45][46][47][48][49][50][51][52] From early Rechargeable lithium-sulfur (Li-S) batteries with the theoretical specifi c energy (≈2600 Wh kg −1 ) have attracted considerable attention due to its favorable prospect for futu...

High utilization and loading of sulfur in cathodes holds the key in the realization of Li-S batteries. We here synthesized a CoN 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 CoN@S delivered a high specific discharge capacity of 1659 mAh g at 0.1 C, almost reaching its theoretic capacity. Also, the battery exhibited a large reversible capacity of about 1100 mAh g at 0.5 C and 1000 mAh g 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. Even at a 94.88% sulfur content, the cathode can still deliver an extremely high specific discharge capacity of 1259 mAh g with good cycle performance.