High-capacity Li2S–graphene oxide composite cathodes with stable cycling performance

Abstract

With its high theoretical capacity of 1166 mA h g À1 , Li 2 S is a promising prelithiated cathode material for applications such as vehicle electrification and grid energy storage. Herein, we demonstrate facile synthesis of Li 2 S-graphene oxide composites for use as high-capacity and stable-cycling Li 2 S cathodes.The wrapping of graphene oxide onto the surface of Li 2 S through favorable lithium-oxygen interactions helps to minimize the dissolution of intermediate polysulfides into the electrolyte during cycling, which is a major reason for rapid capacity decay. Using the Li 2 S-graphene oxide composites as a cathode material, we demonstrate a high discharge capacity of 782 mA h g À1 of Li 2 S ($1122 mA h g À1 of S) with stable cycling performance over 150 charge-discharge cycles.

Two-dimensional layered transition metal disulphides for effective encapsulation of high-capacity lithium sulphide cathodes

“…The above conclusion is supported by disassembly of the cells at various intermediate stages of cycling and testing the electrolyte for sulphur content using inductively coupled plasma-optical emission spectroscopy (ICP-OES; see Methods section for details) 42,47 . Points 1-10 in Fig.…”

“…We see that the Raman spectrum of bare Li 2 S shows the characteristic T 2g peak of Li 2 S at 372 cm À 1 (Fig. 1f) 42,47 . On the other hand, for the Li 2 S@TiS 2 structures, the A 1g peak of TiS 2 at 335 cm À 1 can be clearly seen 58 while the peak of Li 2 S becomes less prominent (Fig.…”

“…Although carbon-based materials are conductive, their nonpolar nature leads to weak interaction with polar Li 2 S and Li 2 S n species 17 , which greatly reduces their ability to bind and confine these species within the shell during cycling. While it is possible to introduce polar oxygen-containing functional groups into carbon to improve its interaction with Li 2 S/Li 2 S n species (for example, by using graphene oxide 42 ), such oxidation treatment decreases the conductivity of carbon drastically. In using carbonbased materials as encapsulation materials for Li 2 S cathodes, there is a major constraint involved: it is difficult to achieve both high conductivity and strong binding with Li 2 S/Li 2 S n species simultaneously.…”

“…Besides acting as a physical barrier, an ideal encapsulation material should also possess strong chemical interaction with polar Li 2 S and Li 2 S n species in order to further bind and confine these species within the shell during cycling. Out of the B16 papers in the literature on encapsulating Li 2 S cathodes thus far, the vast majority (15 of them) use electronically conductive carbon-based materials such as graphene and porous carbon for encapsulation [35][36][37][38][39][40][41][42][43][44][45][46][47][48][49] (the last paper uses Li 3 PS 4 , a lithium superionic conductor/solid electrolyte, which is a poor electronic conductor 50 ). Although carbon-based materials are conductive, their nonpolar nature leads to weak interaction with polar Li 2 S and Li 2 S n species 17 , which greatly reduces their ability to bind and confine these species within the shell during cycling.…”

“…To address these challenges, the typical strategy is to encapsulate Li 2 S cathodes with conductive coating materials in an attempt to improve their conductivity as well as physically entrap intermediate Li 2 S n species within the shell during cycling [35][36][37][38][39][40][41][42][43][44][45][46][47][48][49][50] . Besides acting as a physical barrier, an ideal encapsulation material should also possess strong chemical interaction with polar Li 2 S and Li 2 S n species in order to further bind and confine these species within the shell during cycling.…”