XPS investigations of valence changes during cycling of LiCrMnO₄‐based cathodes in Li‐ion batteries

Abstract

Li-ion batteries have to be improved for high-performance applications especially for automotive application. One aim is the search for new electrode materials with superior properties and their detailed characterization. We used 'quasi in situ' X-ray photoelectron spectroscopy (XPS) to investigate electrode material of the spinel-type LiCrMnO 4 for the cathode during electrochemical cycling. It was found that during charging (de-intercalation of Li from the cathode) chromium is converted from Cr 3+ to Cr 6+ , whereas manganese changes from Mn 4+ to Mn 3+ . Especially when charging to the maximum capacity (at about 5.2 V), this conversion seems to be partially irreversible. The chemical and structural changes connected with this conversion are the possible reason for the irreversible capacity loss at such high charging voltages, which is confirmed by the analysis of the electrode material after 100 charging/discharging cycles.

Binding Energy Referencing for XPS in Alkali Metal-Based Battery Materials Research (II): Application to Complex Composite Electrodes

“…For these materials we also observed nearly no charging when prepared for cathode application as composite with carbon black and PVDF binder. During that work [40,41] no BE correction was made to follow the valence changes for Cr (Cr 3+ / 4+ ) during the intercalation process. For higher charging voltages up to 5.2 V [41], the irreversible formation of Cr 6+ species led to a fast capacity fading during cycling.…”

“…During that work [40,41] no BE correction was made to follow the valence changes for Cr (Cr 3+ / 4+ ) during the intercalation process. For higher charging voltages up to 5.2 V [41], the irreversible formation of Cr 6+ species led to a fast capacity fading during cycling. The intercalated Li was detected at the Li1s position of 54 eV as described for thin film and powder LiCoO 2 [42,43].…”

Influence of annealing temperature on the electrochemical and surface properties of the 5-V spinel cathode material LiCr0.2Ni0.4Mn1.4O4 synthesized by a sol–gel technique

“…6 presents Cr2p spectra normalized with respect to the highest intensity feature at 576 eV attributed to Cr 3+ [40]. There is a peak at 579 eV attributed to Cr 6+ on the surface of the powder annealed at 600°C.…”

X‐Ray Photoelectron Spectroscopy in Analysis of SurfacesUpdate based on the original article by Steffen Oswald,Encyclopedia of Analytical Chemistry, © 2000, John Wiley & Sons, Ltd.

“…(237,239) Figure 26 demonstrates changes at an Li x CrMnO 4 anode material after 100 charging/discharging cycles to reduced (4.88 V) and full (5.2 V) cell voltage. (240) Charging to full voltage (broken line) leads to high starting capacity, but worse reversibility (Figure 26a). Cells charged only to 4.88 V shows good reversibility, but at a lower capacity level.…”