In Situ Electron Paramagnetic Resonance Correlated Spectroscopy and Imaging: A Tool for Lithium-Ion Batteries to Investigate Metallic Lithium Sub-Micrometric Structures Created by Plating and Stripping

Monitoring the formation of dendrites or filaments of lithium is of paramount importance

for Li-based battery technologies, hence the intense activities in designing in situ techniques

to visualize their growth. Herein we report the benefit of correlating in situ electron para4 magnetic resonance (EPR) spectroscopy and EPR imaging to analyze the morphology and

location of metallic lithium in a symmetric Li/LiPF6/Li electrochemical cell during polariza6 tion. We exploit the variations in shape, resonance field and amplitude of the EPR spectra

to follow, operando, the nucleation of sub-micrometric Li particles (narrow and symmetrical

signal) that conjointly occurs with the fragmentation of bulk Li on the opposite electrode

(asymmetrical signal). Moreover, in situ EPR correlated spectroscopy and imaging (spectral10 spatial EPR imaging) allows the identification (spectral) and localization (spatial) of the sub11 micrometric Li particles created by plating (deposition) or stripping (altered bulk Li surface).

We finally demonstrate the possibility to visualize, via in situ EPR imaging, dendrites formed

through the separator in the whole cell. Such a technique could be of great help in mastering

the Li-electrolyte interface issues that plague the development of solid-state batteries.