Three-dimensional spongy framework as superlyophilic,strongly absorbing, and electrocatalytic polysulfide reservoir layer for high-rate and long-cycling lithium-sulfur batteries

摘要

In the development of lithium-sulfur (Li-S) batteries,various approaches have been adopted to enhance the electronic conductivity of the sulfur cathode and alleviate the shuttle effect of polysulfides;however,the strategies providing efficient solutions are still limited.To further improve the electrochemical performance of Li-S batteries,in this work we propose a new strategy involving the incorporation of a three-dimensional functional spongy framework as polysulfide reservoir layer,with strong absorbability and electrocatalytic activity towards sulfur species.The spongy framework has a hierarchical architecture composed of highly conductive Ni foam/graphene/carbon nanotubes/MnO2 nanoflakes (NGCM).The strongly interconnected Ni foam,graphene,and carbon nanotubes of the NGCM sponge facilitate electron transfer during discharge/charge processes;moreover,the superlyophilic properties of the NGCM sponge ensure good wettability and interface contact with the Li-S electrolyte,and the porous MnO2 nanoflakes provide strong chemisorptive and electrocatalytic effects on polysulfides (as confirmed theoretically and experimentally).The NGCM sponge,serving as a polysulfide reservoir layer attached on a conventional sulfur-mixed carbon nanotubes (S/CNTs) cathode,can provide improved reversible capacity,rate capability (593 mAh·g-1 at 3.0 C),and cycling stability.In addition,the self-discharge rate is greatly reduced,owing to the efficient conservation of polysulfides in the NGCM spongy framework.