A proof-of-concept lithium/sulfur liquid battery with exceptionally high capacity density

In this communication, we disclose a proof-of-concept lithium/sulfur liquid battery that has exceptionally high capacity density. In such a battery, the cathode consists of a highly porous carbon cloth (CC) as the cathode current collector and a porous sulfur paper as the source of active material. In the first discharge, sulfur is reduced on the CC surface into high order lithium polysulfide (PS), which dissolves into liquid electrolyte and serves as the catholyte of the so-called “Li/S liquid battery”. By adopting a LiNO3-contained electrolyte to protect Li anode, the Li/S liquid cell is shown to cycle reversibly between 1.7 V and 2.8 V with an initial capacity of 778 mAh g−1 S, corresponding to a capacity density of 10.1 mAh cm−2 CC, which could be the highest capacity density among the rechargeable Li/S batteries reported ever. This work reveals that the high capacity density Li/S batteries can be made through a “Li/S liquid cell” by employing a highly porous carbon electrode to accommodate the insoluble sulfur reduction products (Li2S2/Li2S) with appropriate protection of the Li anode.

► A Li/S liquid cell with two-layer structural cathode is proposed for high capacity density.
► Initial mixing state of sulfur and carbon in cathode is not important for a Li/S liquid cell.
► High surface area carbon and solvent with high polysulfide solubility favor cell performance.
► Effective improvement on Li/S cell should be on the Li anode, instead of the cathode.