Supercritical CO2 Synthesis of Freestanding Se1-x S x Foamy Cathodes for High-Performance Li-Se1-x S x Battery.

Chengwei Lu,Kun Wang,Wenkui Zhang,Xinping He,Yongping Gan,Yang Xia,Ruyi Fang,G Gnana Kumar,Hui Huang,Zhen Xiao

doi:10.3389/fchem.2021.738977

Abstract

Selenium-sulfur solid solutions (Se1-xSx) are considered to be a new class of promising cathodic materials for high-performance rechargeable lithium batteries owing to their superior electric conductivity than S and higher theoretical specific capacity than Se. In this work, high-performance Li-Se1-xSx batteries employed freestanding cathodes by encapsulating Se1-xSx in a N-doped carbon framework with three-dimensional (3D) interconnected porous structure (NC@SWCNTs) are proposed. Se1-xSx is uniformly dispersed in 3D porous carbon matrix with the assistance of supercritical CO2 (SC-CO2) technique. Impressively, NC@SWCNTs host not only provides spatial confinement for Se1-xSx and efficient physical/chemical adsorption of intermediates, but also offers a highly conductive framework to facilitate ion/electron transport. More importantly, the Se/S ratio of Se1-xSx plays an important role on the electrochemical performance of Li- Se1-xSx batteries. Benefiting from the rationally designed structure and chemical composition, NC@SWCNTs@Se0.2S0.8 cathode exhibits excellent cyclic stability (632 mA h g−1 at 200 cycle at 0.2 A g−1) and superior rate capability (415 mA h g−1 at 2.0 A g−1) in carbonate-based electrolyte. This novel NC@SWCNTs@Se0.2S0.8 cathode not only introduces a new strategy to design high-performance cathodes, but also provides a new approach to fabricate freestanding cathodes towards practical applications of high-energy-density rechargeable batteries.

Highlights

Lithium-sulfur (Li-S) batteries are considered as promising next-generation electrochemical energystorage systems in view of their high theoretical energy density (2600 W h kg−1), environmental friendliness and natural richness of sulfur (Yao et al, 2017; Zheng et al, 2020; Yuan et al, 2021a; Yuan et al, 2021b; Sun et al, 2021)
Selenium is a semiconductor with much higher electronic conductivity (1 × 10−3 S m−1) than sulfur, which is conducive to excellent kinetic behavior (Zhang et al, 2020)
Local magnification SEM images (Figures 2B,C) demonstrate that numerous interlaced SWCNTs are covered the surface of melamine foam derived carbon skeletons, as well as SWCNTs are formed into small sheets between carbon skeletons

Summary

Introduction

Lithium-sulfur (Li-S) batteries are considered as promising next-generation electrochemical energystorage systems in view of their high theoretical energy density (2600 W h kg−1), environmental friendliness and natural richness of sulfur (Yao et al, 2017; Zheng et al, 2020; Yuan et al, 2021a; Yuan et al, 2021b; Sun et al, 2021). Research shows heteroatomdoped (B, N, O, etc.) carbon hosts can effectively improve the electrochemical performance of Li-Se1-xSx batteries due to the strong chemical affinity of polarized carbon surface, which can significantly trap the soluble intermediates to inhibit the shuttle effect and side reactions in the electrolyte (Guo et al, 2016; Zhang et al, 2017; Fan et al, 2018; He et al, 2018; Sun et al, 2021).

Results

Conclusion