Evolving affinity between Coulombic reversibility and hysteretic phase transformations in nano-structured silicon-based lithium-ion batteries

Ken Ogata ,Y S Kim,J H Kim,Y.-H Cho,H.-G Kim,Ji‐Hyun Jang ,Yoshimi Kubo ,Sang Eun Jeon ,Wonchang Choi ,Shunsuke Saito ,Meiten Koh ,Yoohwa Hwang ,Seok Gwang Doo ,Ho Seok Park ,Dong-Su Ko ,Kohei Uosaki ,In‐Sun Jung ,Kazushi Ito ,Koichi Takei ,Sangil Han

doi:10.1038/s41467-018-02824-w

Abstract

Nano-structured silicon is an attractive alternative anode material to conventional graphite in lithium-ion batteries. However, the anode designs with higher silicon concentrations remain to be commercialized despite recent remarkable progress. One of the most critical issues is the fundamental understanding of the lithium–silicon Coulombic efficiency. Particularly, this is the key to resolve subtle yet accumulatively significant alterations of Coulombic efficiency by various paths of lithium–silicon processes over cycles. Here, we provide quantitative and qualitative insight into how the irreversible behaviors are altered by the processes under amorphous volume changes and hysteretic amorphous–crystalline phase transformations. Repeated latter transformations over cycles, typically featured as a degradation factor, can govern the reversibility behaviors, improving the irreversibility and eventually minimizing cumulative irreversible lithium consumption. This is clearly different from repeated amorphous volume changes with different lithiation depths. The mechanism behind the correlations is elucidated by electrochemical and structural probing.

Highlights

Nano-structured silicon is an attractive alternative anode material to conventional graphite in lithium-ion batteries
On every 20th cycle, all electrodes are slowly cycled under DOD100% regardless of the depth of discharge (DOD) value used in previous cycles, in order to capture the structural characteristics for the full potential range (Fig. 1c)
TEM (Figs. 5 and 6), X-ray diffraction (XRD) (Fig. 6), MAS ss-NMR (Fig. 7), and X-ray absorption fine structure (XAFS) (Fig. 8) methods are further used to reveal the mechanism associated with the reversibility

Summary

Introduction

Nano-structured silicon is an attractive alternative anode material to conventional graphite in lithium-ion batteries. Repeated latter transformations over cycles, typically featured as a degradation factor, can govern the reversibility behaviors, improving the irreversibility and eventually minimizing cumulative irreversible lithium consumption This is clearly different from repeated amorphous volume changes with different lithiation depths. New in situ and ex situ analytical methods have helped to understand the underlying mechanisms[17,18,19,20,21,22,23,24,25,26,27,28,29,30] These studies show that crystalline-Si (c-Si) is converted into amorphous-LixSi (a-LixSi) phases during the first lithiation, which involves large asymmetric volume changes[22] owning to different Li reaction rate constants at different c-Si facets[31]. Electrolyte can still invade due to the transport of Li ions (coupled with organic components) and/

Methods

Results

Conclusion