Switchable encapsulation of polysulfides in the transition between sulfur and lithium sulfide

Yongsheng Fu,Yifei Yuan,Lei Yuan,Erjun Kan,Lei Yu,Wuxin Bai,Xiaoping Ouyang,Xin Wang,Zhen Wu,Yingjie Lan,Chengxi Huang,Junwu Zhu,Jun Lu,Qiurui Han,Peng Chen

doi:10.1038/s41467-020-14686-2

Abstract

Encapsulation strategies are widely used for alleviating dissolution and diffusion of polysulfides, but they experience nonrecoverable structural failure arising from the repetitive severe volume change during lithium−sulfur battery cycling. Here we report a methodology to construct an electrochemically recoverable protective layer of polysulfides using an electrolyte additive. The additive nitrogen-doped carbon dots maintain their “dissolved” status in the electrolyte at the full charge state, and some of them function as active sites for lithium sulfide growth at the full discharge state. When polysulfides are present amid the transition between sulfur and lithium sulfide, nitrogen-doped carbon dots become highly reactive with polysulfides to form a solid and recoverable polysulfide-encapsulating layer. This design skilfully avoids structural failure and efficiently suppresses polysulfide shuttling. The sulfur cathode delivers a high reversible capacity of 891 mAh g−1 at 0.5 C with 99.5% coulombic efficiency and cycling stability up to 1000 cycles at 2 C.

Highlights

Encapsulation strategies are widely used for alleviating dissolution and diffusion of polysulfides, but they experience nonrecoverable structural failure arising from the repetitive severe volume change during lithium−sulfur battery cycling
To study the optical properties of the as-prepared nitrogen-doped carbon dots (N-CDs), photoluminescence measurements for the N-CDs in aqueous solution were carried out using different excitation wavelengths (Supplementary Fig. 1)
Photoluminescence spectra of N-CDs show the strongest intensity at 380 nm excitation

Summary

Introduction

Encapsulation strategies are widely used for alleviating dissolution and diffusion of polysulfides, but they experience nonrecoverable structural failure arising from the repetitive severe volume change during lithium−sulfur battery cycling. To further enhance the interaction with polar LiPS, polar materials such as functionalized carbon materials (aminomodified reduced graphene oxide, nitrogen-doped mesoporous carbon), metal oxides, metal carbides, metal sulfides, metal nitrides, and polyoxometalates have been investigated due to their strong chemical adsorption capacities[16,17,18,19,20,21,22,23,24,25,26,27] These encapsulation strategies are generally effective at alleviating LiPS dissolution. The recoverable processes of thrombus formation and thrombolysis in the blood vessel inspired us to explore a unique LiPS encapsulation strategy where a skilfully designed electrolyte additive (analogous to the platelet) can interact only with LiPS to form a recoverable protective layer in situ. The LiPS “clotting factors” (LiPSCFs) additive should meet at least three criteria: good dispersibility in the electrolyte, strong interaction with LiPS, and excellent restraining ability of the recoverable protective layer for the subsequent dissolution of LiPS

Methods

Results

Conclusion