Atomic visualization of a non-equilibrium sodiation pathway in copper sulfide

Jae Yeol Park,Jae Yeol Park,Joon Ha Chang,Joon Ha Chang,Hyeon Kook Seo,Jong Min Yuk,Jeong Yong Lee,Jeong Yong Lee,Sung Joo Kim,Sung Joo Kim,Hyeon Kook Seo

doi:10.1038/s41467-018-03322-9

Abstract

Sodium ion batteries have been considered a promising alternative to lithium ion batteries for large-scale energy storage owing to their low cost and high natural abundance. However, the commercialization of this device is hindered by the lack of suitable anodes with an optimized morphology that ensure high capacity and cycling stability of a battery. Here, we not only demonstrate that copper sulfide nanoplates exhibit close-to-theoretical capacity (~560 mAh g–1) and long-term cyclability, but also reveal that their sodiation follows a non-equilibrium reaction route, which involves successive crystallographic tuning. By employing in situ transmission electron microscopy, we examine the atomic structures of four distinct sodiation phases of copper sulfide nanoplates including a metastable phase and discover that the discharge profile of copper sulfide directly reflects the observed phase evolutions. Our work provides detailed insight into the sodiation process of the high-performance intercalation–conversion anode material.

Highlights

Sodium ion batteries have been considered a promising alternative to lithium ion batteries for large-scale energy storage owing to their low cost and high natural abundance
This affects the reaction kinetics of CuS and causes a reaction to deviate from thermodynamic equilibrium
We visualize the entire process at the atomic scale by employing high-resolution transmission electron microscopy (HR-TEM)

Summary

Introduction

Sodium ion batteries have been considered a promising alternative to lithium ion batteries for large-scale energy storage owing to their low cost and high natural abundance. The reaction mechanism cannot be considered so simple because the discharge profile of CuS shows more reaction plateaus than lithiation It has been reported in many intercalation reaction systems that Na insertion experiences a higher diffusion barrier than Li due to the large ionic and atomic radii of Na that introduce large local strain to the host lattice[10,11,12]. We visualize the entire process at the atomic scale by employing high-resolution transmission electron microscopy (HR-TEM) This technique allows us to identify multiple distinct phases at various reaction stages and determine the reaction kinetics by quantitative imaging analysis. This study, using a high-resolution technique, provides in-depth knowledge on the unique electrochemistry of a SIB electrode

Methods

Results

Conclusion