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

Li, Qing; Ma, Zhipeng; Li, Jiaojiao; Liu, Zhan; Fan, Lukai; Qin, Xiujuan; Shao, Guangjie

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