LiMn₂O₄ Surface Chemistry Evolution during Cycling Revealed by in Situ Auger Electron Spectroscopy and X-ray Photoelectron Spectroscopy

Abstract

This work utilizes in situ electrochemical and analytical characterization during cycling of LiMnO (LMO) equilibrated at different potentials in an ultrahigh vacuum (UHV) environment. The LMO reacts with organic molecules in the vacuum to form a high surface concentration of LiCO (≈50% C) during initial charging to 4.05 V. Charging to higher potentials reduces the overall LiCO concentration (≈15% C). Discharging to 3.0 V increases the LiCO concentration (≈30% C) and over discharging to 0.1 V again reduces its concentration (≈15% C). This behavior is reproducible over 5 cycles. The model geometry utilized suggests that oxygen from LMO can participate in redox of carbon, where LMO contributes oxygen to form the carbonate in the solid electrolyte interphase (SEI). Similar results were obtained from samples cycled ex situ, suggesting that the model in situ geometry provides reasonably representative information about surface chemistry evolution. Carbon redox at LMO and the inherent voltage instability of the LiCO likely contributes significantly to its capacity fade.

Correlation between manganese dissolution and dynamic phase stability in spinel-based lithium-ion battery

“…The surface oxidation states of Mn were then examined by X-ray photoelectron spectroscopy (XPS) with a shallow detection scale (<3 nm). Figure 6c shows Mn 2p 1/2 and 2p 3/2 peaks of two samples at 640.9 and 653.1 eV, consistent with the data reported before 55,56 . Further fitting results showed that Mn 4+ respectively occupied 47% and 59% of the LMO and LR-LMO sample surfaces (Fig.…”

The effect of electrochemical cycling on the strength of LiCoO2

“…We hypothesize that heterogeneously delithiating a single plane can induce a larger effect, than was previously calculated for homogeneous delithiation by Wu and Zhang . Results of Li NMR indicate that these point defects are heterogeneously distributed, suggesting that this hypothesis is reasonable. Calculations similar to those in Ref.…”

“…However, processes inducing capacity fade are many and often interrelated . For example, mechanical degradation, surface reactions, gas evolution, loss of percolation, Li interactions with inactive components, corrosion, and their interactions have been associated with capacity fade . Mechanical degradation and fracture has received considerable attention, as particle fracture can lead to electronic and/or ionic isolation of a portion of the active material .…”

In-operando photoelectron spectroscopy for batteries: Set-up using pristine thin film cathode and first results on NaxCoO2

“…Such reactions were observed to a much higher extend by the authors using model cells assembled within a glovebox and transferred to an UHV system. 18,34…”