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arXiv · 2002.04843

Tracking the diffusion-controlled lithiation reaction of LiMn2O4 by in-situ TEM

Torben Erichsen·Björn Pfeiffer·Vladimir Roddatis·Cynthia A. Volkert
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Abstract

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.

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Torben Erichsen, Björn Pfeiffer, Vladimir Roddatis, Cynthia A. Volkert. 2020-02-12. Tracking the diffusion-controlled lithiation reaction of LiMn2O4 by in-situ TEM. https://arxiv.org/abs/2002.04843

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