The demand for higher energy density in Li-ion batteries have resulted in a progressive shift from purely graphitic carbon electrodes to composite materials involving a combination of graphite (Gr) and silicon oxide (SiOx). The presence of two active materials with distinct open circuit voltages results in an uneven lithiation during cycling, causing a disparate use of each active material [1]. Being able to quantify the differences in lithiation becomes of high importance in order to understand and quantify performance and aging of this class of materials.

This study aims at the development of a methodology for the characterization and quantification of the lithiation of composite (Gr-SiOx) negative electrodes. This is performed by ex-situ measurements with solid-state 7Li NMR spectroscopy, a technique that can identify lithium in different environments [2]. This will enable for quantification of lithiation of both active materials with a single and direct (that is, in detecting lithium) measurement. Some studies characterized these processes by operando XRD measurements [3, 4], deriving a measure of lithium content in graphite from the changes in the crystal structure of the material. The possibility of quantification with a direct measurement, is relevant for its application in post-mortem analysis of high energy Li-ion batteries aimed at identifying spatial heterogeneities in their degradation [5]. Ex-situ XRD measurements have been performed on the same samples to further correlate this method with the existing literature.

The method has been developed and validated by studying the lithiation of a commercial electrode containing 15 vol% of SiOx and will be further applied in the characterization of the performances of materials coming from a commercial 4695 cell which will serve as a basis for the ongoing aging studies in the same batch of cells.