In-Situ Solid State NMR for Characterizing Battery Materials

Abstract

The demand for inherently safe, large capacity, high-rate capability energy storage has led to the investigation of a class of metallic and semi-metallic elements that form stable intermetallics with lithium, providing Li+ storage capacities of three to ten times that of today’s lithium-ion batteries. Unfortunately, such high capacity intermetallic anodes undergo structural transformations from crystalline to amorphous states with large volume expansions upon intercalation, changing the anode's microstructure and local chemical environments, which lead to reduced capacity. Because of their amorphous nature, the atomic-level structures of the intermetallic are not amenable to study by conventional diffraction techniques. Solid-state nuclear magnetic resonance (NMR) spectroscopy is an ideal technique to probe amorphous materials and understand how kinetically driven compositional changes affect the material microstructure and the local chemical environment. We have measured the 7Li and 119Sn NMR spectra of electrochemically lithiated tin ex-situ and have identified a number of different lithium environments. Furthermore, we have measured in-situ 7Li NMR spectra as a function of lithiation and de-lithiation of different materials, including graphitic carbon, silicon, and tin. We will discuss the findings and their implications for the design of various nanostructured intermetallic anodes.