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 (LiS, 4 ≤ x ≤ 8), we present an effective strategy to incorporate sulfiphilic metal ion (Cu) with high-binding energy to LiS into the framework. Through a one-step hydrothermal method, Cu is homogeneously dispersed in Al-MOF, producing a bimetallic Al/Cu-MOF as advanced cathode material. The macroscopic LiS 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/Cu-MOF (Al/Cu-MOF-S). The assembled Li-S batteries with Al/Cu-MOF-S yield improved cyclic performance, much better than that of monometallic Al-MOF 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 into porous MOF, will provide a novel and powerful approach for efficient sulfur host materials.