Core-Shell-Structured Sulfur Cathode: Ultrathin δ-MnO2 Nanosheets as the Catalytic Conversion Shell for Lithium Polysulfides in High Sulfur Content Lithium-Sulfur Batteries

Owing to their low cost and high theoretical energy density, lithium-sulfur (Li -S) batteries are highly promising as a contender for the post-lithium-ion battery era. However, the intrinsic low reversible conversion ability of lithium polysulfides to sulfur/Li2S during charging/discharging seriously hinders the sulfur utilization, resulting in poor cycling life of batteries. Herein, we report an improvement of core-shell-structured sulfur nanospheres@ultrathin delta-MnO2 nanosheet electrode materials prepared by a simple precipitation reaction method, in which the ultrathin delta-MnO2 nanosheets as a catalytic layer can promote the chemical adsorption of lithium polysulfides and their conversion rates to sulfur/Li2S. Using a combination of the UV-visible adsorption spectra and first-principles calculation, the results indicate that the Mn-O coordination center on the surface of the MnO2 structure plays an efficient catalytic role in the conversion reaction of lithium polysulfides to insoluble S/Li2S. The sulfur nanospheresgultrathin delta-MnO2 nanosheet composite with a high S mass ratio of 82 wt % reveals a high specific capacity of 846 mA h g(-1) at 1 C rate and good cycling stability. Moreover, the areal capacity of the electrode with a high sulfur loading mass of 10 mg cm(-2). is 5.2 mA h cm(-2), approaching the practical application standard at a current density of 1 mA cm(-2).