Utilization of 29Si MAS-NMR to Understand Solid State Diffusion in Energy Storage Materials

Fulya Dogan,Baris Key,John T Vaughey

doi:10.3389/fceng.2022.833162

Fulya Dogan, Baris Key + Show 1 more

Open Access

https://doi.org/10.3389/fceng.2022.833162

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Abstract

The properties of many solid-state materials arise from critical interfaces tied to the structure, morphology, and composition of the materials under study. For many materials, identifying components that may be invisible to diffraction techniques or other bulk sensitive techniques (i.e. inductively coupled plasma (ICP)), may cause important information to be overlooked. These can include grain boundary phases, nanoscale coatings, amorphous layers, or second phases that influence the materials environment. In this short review, the use of 29Si MAS NMR as a local probe to detect silicon-containing phases in complex energy storage systems is explored with a focus is on silicon-containing materials and silicon electrodes. Examples highlighting the utility of 29Si MAS NMR include 1) examining copper diffusion into silicon as a method to create 3 dimensional electrodes, 2) using Mg(II) electrolyte additives to create in-situ nanoscale silicide coatings to inhibit low voltage parasitic side reactions and extend calendar life, and 3) studying the lithiation reactions of passivated silicon on different time scales.

Highlights

Understanding solid-state diffusion is critical to understanding the role of syntheses in areas ranging from materials processing to the creation of protective coatings
Uses that require silica free materials require more stringent handling due to this oxyphilic nature of the silicon surfaces (Jiang et al, 2019; Schulze et al, 2021). It was noted by Edström et al, that this natural silica-based coating on silicon is lithiated early in the process forming a variety of lithium silicates, notably Li4SiO4 (Philippe et al, 2012; Philippe et al, 2013a)
While diffusion is an important aspect of many commercial systems, methods to understand these properties at a mechanistic level are often limited to an understanding of crystalline pathways available to the diffusing species

Summary

INTRODUCTION

Understanding solid-state diffusion is critical to understanding the role of syntheses in areas ranging from materials processing to the creation of protective coatings (van der Ven et al, 2013). Previous diffraction studies showed formation of the electrochemically inactive phase Cu3Si for samples heated above 700°C but the isolation of disordered (lacking long-range order) or amorphous species (i.e., nanoscale silicon oxides, surface silicon hydrides/ hydroxides) was not possible using XRD methods (Joyce et al, 2012). Identifying these interfacial phases is important in understanding the electrode properties as many silicon oxides are insulating and electrochemically inactive. Using 29Si {1H} CP MAS NMR allowed the selective investigation and detection of the 29Si NMR resonances from silicon atoms in close proximity to protons and surface silicon atoms

Background

CONCLUSION