Bimetallic Metal-Organic Framework with High-Adsorption Capacity toward Lithium Polysulfides for Lithium–sulfur Batteries

The practical application of Li-S batteries is largely impeded by the“shuttle effect”generated at the cathode which results in a short life cycle of the battery.To address this issue,this work discloses a bimetallic metal-organic framework(MOF)as a sulfur host material based on Al-MOF,commonly called(Al)MIL-53.To obtain a high-adsorption capacity to lithium polysulfides(Li_(2)S_(x),4≤x≤8),we present an effective strategy to incorporate sulfiphilic metal ion(Cu^(2+))with high-binding energy to Li_(2)S_(x) into the framework.Through a one-step hydrothermal method,Cu^(2+) is homogeneously dispersed in Al-MOF,producing a bimetallic Al/Cu-MOF as advanced cathode material.The macroscopic Li2S4 solution permeation test indicates that the Al/Cu-MOF has better adsorption capacity to lithium polysulfides than monometallic Al-MOF.The sulfur-transfusing process is executed via a melt-diffusion method to obtain the sulfur-containing Al/CuMOF(Al/Cu-MOF-S).The assembled Li-S batteries with Al/Cu-MOF-S yield improved cyclic performance,much better than that of monometallic AlMOF as sulfur host.It is shown that chemical immobilization is an effective method for polysulfide adsorption than physical confinement and the bimetallic Al/Cu-MOF,formed by incorporation of sulfiphilic Cu^(2+) into porous MOF,will provide a novel and powerful approach for efficient sulfur host materials.

Bonding VSe2 ultrafine nanocrystals on graphene toward advanced lithium-sulfur batterie

Lithium–sulfur batteries have been attracting considerable research attention due to their high energy densities and low costs. However, one of their main challenges is the undesired shuttling of polysulfides, causing rapid capacity degradation. Herein, we report the first example of sulfiphilic VSe2 ultrafine nanocrystals immobilized on nitrogen-doped graphene to modify the battery separator for alleviating the shuttling problem. VSe2 nanocrystals provide numerous active sites for chemisorption of polysulfides as well as benefit the nucleation and growth of Li2S. Furthermore, the kinetic reactions are accelerated which is confirmed by higher exchange current density and higher lithium ion diffusion coefficient. And the first-principles calculations further show that the exposed sulfiphilic planes of VSe2 boost the redox of Li2S. When used as separators within the lithium sulfur batteries, the cell indicates greatly enhanced electrochemical performances with excellent long cycling stability and exceptional rate capability up to 8 C. Moreover, it delivers a higher areal capacity of 4.04 mAh·cm^−2 as well as superior cycling stability with sulfur areal loading up to 6.1 mg·cm^−2. The present strategy can encourage us in engineering novel multifunctional separators for energy-storage devices.