Operando X-ray Absorption Spectroscopy and Emission Kβ_1,3 Study of the Manganese Redox Activity in High-Capacity Li₄Mn₂O₅ Cathode

Abstract

The electrochemical performance of nanostructured Li4Mn2O5 (or rather the 0.93Li3.6–x Mn2.4O5.4–0.07Li2O composite) displaying an outstanding charge capacity of 350 mA h/g was recently reported. Interestingly, the removal of lithium from Li4Mn2O5 is found to take place beyond the oxidation limit of +4 for Mn in an octahedral environment. To characterize the nature of this extra capacity, we have approached the study of the redox chemistry and local structure of manganese in Li4Mn2O5 via a combination of X-ray absorption and emission spectroscopies at the manganese K-edge. To support our results, we have thoroughly characterized the composition of the materials at several potential values by inductively coupled plasma and online electrochemical mass spectrometry. Additionally, operando X-ray absorption near-edge structure studies, in excellent agreement with ex situ data, were carried out for the charge and discharge of the battery. Our results unequivocally rule out the participation of the Mn4+/Mn5+ redox couple and indicate the participation of oxygen in the electrochemistry. After the first charge, the battery cycles reversibly between the charged and discharged states, where the lithium exchange is mainly compensated by anionic redox.

Li2O:Li–Mn–O Disordered Rock‐Salt Nanocomposites as Cathode Prelithiation Additives for High‐Energy Density Li‐Ion Batteries

“…Figure shows a solid solution behavior of the RS with a continuous evolution of the lattice parameters over the 1.5–4.5 V potential window, in agreement with previous in situ XANES and ex situ total scattering studies. The lattice parameter evolution, quantified by the sequential Rietveld refinement of over 100 in situ data sets, mimics the shape of the electrochemical curve.…”

“…7% and 35% Li 2 O composites were studied over the course of one and two charge/ discharge cycles in Figure 2 while for the 55 mol% Li 2 O-richest composite, only 20% of the first charge was recorded (see Figures S3 and S4 in the Supporting Information for in situ total scattering and ex situ diffraction and X-ray absorption near-edge spectroscopy (XANES) data for the pristine and charged at 4.5 V samples). Figure 2 shows a solid solution behavior of the RS with a continuous evolution of the lattice parameters over the 1.5-4.5 V potential window, in agreement with previous in situ XANES [29] and ex situ total scattering [28] studies. The lattice parameter evolution, quantified by the sequential Rietveld refinement of over 100 in situ data sets, mimics the shape of the electrochemical curve.…”

“…The nonlinear evolution of Mn-Mn interatomic distances with Li concentration in 0.07Li 2 O:0.93Li 2/3 Mn 1/3 O 5/6 previously characterized by extended X-ray absorption fine structure, [29] is in good agreement with the refined lattice parameters in Figure 2a Figure S7 in the Supporting Information for the refined phase wt%), and no traces of other crystalline or amorphous secondary phases could be detected. After the first charge, Li 2/3−x Mn 1/3 O 5/6 cycles reversibly between charged and discharged states with an exchange of ≈0.4 Li per formula unit without the further participation of Li 2 O.…”

“…The nonlinear evolution of Mn–Mn interatomic distances with Li concentration in 0.07Li 2 O:0.93Li 2/3 Mn 1/3 O 5/6 previously characterized by extended X‐ray absorption fine structure, is in good agreement with the refined lattice parameters in Figure a. The unit cell of the active RS phase contracts from 4.158(2) to 4.070(2) Å with the extraction of lithium after the first charge at 4.5 V, and expands to 4.126(1) Å during cell discharge.…”

Interfacial Degradation and Optimization of Li‐rich Cathode Materials†

“…used operando X‐ray absorption near‐edge structure to study the redox chemistry and local structure of manganese in Li 4 Mn 2 O 5 . [ 130 ] In a broadening of the XANES features as a function of the lapsed time, the white line moves to higher energies upon charging at the same potential. This result indicated the disordering structure increasing and the structural amorphization.…”