Highly Nitridated Graphene–Li 2 S Cathodes with Stable Modulated Cycles

To understand the actual electrochemical activation processes, we developed in situ scanning electron microscopy (SEM) and transmission electron microscopy (TEM) techniques to study the cathode material structural changes on delithiation.

In situ electronic microscopy set-ups and the characterization results during delithiation of Li₂S.

a,b) A newly developed electrochemical microcell for in situ SEM.

 c) Time-lapse SEM images of the activation process of Li₂S on a single-layered graphene electrode in a standard LiTFSIDOL/DME electrolyte (also see Movie 1, Supporting Information). Red color shows a relatively thicker Li₂S layer on graphene. The Li₂S particles on graphene became smaller and smaller during the delithiation activation process, which was due to the continuous dissolution of the intermediate lithium polusulfides into the electrolyte (see schematic diagram below). Scale bar: 20 µm.

d,e) An in situ TEM electrochemical characterization set-up.

 f) Time-lapse TEM images of the activation process of HNG−Li₂S in an ionic liquid based electrolyte (Movie 2, Supporting Information). Similarly, the generated intermediate lithium polysulfi des during delithiation process gradually dissolved in the electrolyte, causing the aggregation of the HNG sheets and the remaining lithium sulfi de or polysulfi des. Scale bar: 50 nm.

The in-situ electrochemical chip designed in this study use an open electrochemical chip technology independently developed and produced by YW MEMS (Suzhou) Co., Ltd. The technology uses ionic liquid electrolyte. When the user uses it, the lithium electrode sheet is fixed at one end of the chip in the glove box, and then the other electrode sample is fixed on the gold wire. The ionic liquid electrolyte will soaked between the sample and the lithium battery, thus forming the whole in situ battery system. The electrode sample soaked in ionic liquid at the edge of gold wire can be observed directly in transmission electron microscope, and enables high-resolution in situ real-time observation.

Original link: DOI: 10.1002/aenm.201501369