Spinel lithium manganese oxide (LixMn2O4) is used as an active material in battery cathodes. It is a relatively inexpensive and environmentally friendly material, but suffers from capacity fade during use. The capacity losses are generally attributed to the formation of the tetragonal phase (x > 1) due to overpotentials at the surfaces of the micron-sized particles that are used in commercial electrodes. In this study, we investigate the mechanisms of tetragonal phase formation by performing electrochemical lithiation (discharging) in-situ in the transmission electron microscope (TEM) utilizing diffraction and high resolution as well as spectroscopy. We observe a sharp interface between the cubic spinel (x = 1) and the tetragonal phase (x = 2), that moves under lithium diffusion-control. The tetragonal phase forms as a complex nanotwinned microstructure, presumably to relieve the stresses due to expansion during lithiation. We propose that the twinned microstructure stabilizes the tetragonal phase, adding to capacity loss upon deep discharge.
@article{arxiv.2002.04843,
title = {Tracking the diffusion-controlled lithiation reaction of LiMn2O4 by in-situ TEM},
author = {Torben Erichsen and Björn Pfeiffer and Vladimir Roddatis and Cynthia A. Volkert},
journal= {arXiv preprint arXiv:2002.04843},
year = {2020}
}
Comments
31 pages, 7 figures plus additional SI, submitted to ACS Nano