Comprehensive Approach to Investigate the De-/Lithiation Mechanism of Fe-Doped SnO2 as Lithium-Ion Anode Material

Abstract

Iron-doped tin oxide (Sn0.9Fe0.1O2), and specifically carbon-coated Sn0.9Fe0.1O2 (Sn0.9Fe0.1O2-C) provides high reversible capacity and a reasonably low de-/lithiation potential owing to the combined conversion and alloying mechanism. The initial (quasi-)amorphization during the first lithiation, however, renders an in-depth understanding of the reaction mechanism challenging. Herein, a comprehensive investigation via a set of highly complementary characterization techniques is reported, including operando X-ray diffraction, ex situ 119Sn and 57Fe Mössbauer spectroscopy, ex situ 7Li NMR spectroscopy, operando isothermal microcalorimetry (IMC) of Li‖Sn0.9Fe0.1O2-C coin cells, and electrochemical microcalorimetry of single Sn0.9Fe0.1O2-C electrodes. The combination of these advanced techniques allows for detailed insights into the lithiation and delithiation mechanism and the potential determining processes, despite the (quasi-) amorphous nature of the active material after the initial lithiation.