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

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. [Figure not available: see fulltext.].