The Decoupling of Solid-Electrolyte Interphase Formation from the Mechanical Deformation of Silicon Electrodes

Abstract

The reduction of electrolyte is well known to result in the formation of the solid electrolyte interphase (SEI) at the interface of electrolyte and silicon electrodes which determines the reversibility of lithium ion battery chemistry. The SEI formation is usually coupled with the mechanical deformation of silicon electrode because of its large volume changing of about 300% during the cycling lithiation and delithiation. We may know more about the chemistry of SEI by decoupling it from the silicon mechanical deformation. In this talking, we will present a novel electrochemical methodology having achieved this decoupling which results in a special surface species - “early-stage SEI”. The chemistry of the early-stage SEI was well studied to distinguish the following challenging questions: Can the early-stage SEI passivate the silicon surface? How is the stability of the early-stage SEI during the long rest in the electrolyte? In comparison with the regular SEI coupled by the mechanical deformation of silicon, the early-stage SEI was found with a lot of new chemistry by using the characterization of X-ray Photoelectron Spectroscopy (XPS), Atomic Force Microscopes-Scanning Spreading Resistance Microscopy (AFM-SSRM). The composition of early-stage SEI was verified by XPS to include lithium ethylene dicarbonate (LiEDC) and lithium carbonate (Li2CO3). Meanwhile, the silicon was verified without lithiation behavior. The evolution of surface roughness and electrical conductivity of early-stage SEI was addressed by AFM-SSRM. This study may gain much attention due of the fundamental understanding of the silicon electrode surface chemistry with potential application in lithium ion battery of high energy density.