Phase evolution and structural modulation during in situ lithiation of MoS2, WS2 and graphite in TEM

Chanchal Ghosh,Avinash M Dongare,C Barry Carter,Arthur Dobley,Matthew T Janish,Shayani Parida,Manish Kumar Singh

doi:10.1038/s41598-021-88395-1

Abstract

Li-ion batteries function by Li intercalating into and through the layered electrode materials. Intercalation is a solid-state interaction resulting in the formation of new phases. The new observations presented here reveal that at the nanoscale the intercalation mechanism is fundamentally different from the existing models and is actually driven by nonuniform phase distributions rather than the localized Li concentration: the lithiation process is a ‘distribution-dependent’ phenomena. Direct structure imaging of 2H and 1T dual-phase microstructures in lithiated MoS2 and WS2 along with the localized chemical segregation has been demonstrated in the current study. Li, a perennial challenge for the TEM, is detected and imaged using a low-dose, direct-electron detection camera on an aberration-corrected TEM and confirmed by image simulation. This study shows the presence of fully lithiated nanoscale domains of 2D host matrix in the vicinity of Li-lean regions. This confirms the nanoscale phase formation followed by Oswald ripening, where the less-stable smaller domains dissolves at the expense of the larger and more stable phases.

Highlights

Li-ion batteries function by Li intercalating into and through the layered electrode materials
The selected area electron diffraction pattern (SADP) as shown in Fig. 1(a) confirms the specimen has been oriented along [1 0 1 1] zone axis during imaging
The atomic-resolution transmission electron microscopy (TEM) image confirms the structure of the specimen as 2H-MoS2 and is essential as a reference to compare the phase after interaction with Li

Summary

Introduction

Li-ion batteries function by Li intercalating into and through the layered electrode materials. The alkali ions interact with the host matrix leading to significant changes in the microstructural and microchemical nature of the layered m aterials[22,23,24,25]. Transmission electron microscopy (TEM) and its associated techniques have been extensively used to study the modified structural and chemical nature of the intercalated m atrices[26,27]. In situ interactions between the alkali ions and layered materials inside the TEM is the only technique that allows the direct visualization of the structural changes as well as associated morphological changes in real time[32,33,34,35]. Technique in this regard and is more likely to mimic the operando behavior of the electrochemical storage c ell[36,37,38]

Methods

Results

Conclusion