Structural and electrochemical properties of iron- and nickel-substituted Li 2 MnO 3 cathodes in charged and discharged states

Doping Li-rich cathode material Li2MnO3 : Interplay between lattice site preference, electronic structure, and delithiation mechanism

“…These results are thus in agreement with the corresponding doped Li 2 MnO 3 compositions observed in experiments. [8][9][10]15,16 Yu et al, 8 for example, reported that Mg occupies the Li (4h) site in Li 2 MnO 3 , which is consistent with the results for Mg. We note that, though Mg + Li has the same energy at the 4h site and the 2c site as mentioned above, its concentration at 4h is higher than that at 2c because the number of the 4h sites in the supercell is twice that of the 2c sites.…”

“…Fe − Mn , as isolated defect, can occur in the form of Fe 0 Mn (i.e., Fe 4+ at the Mn site); in this case, Fe changes its charge state from +3 to +4 to maintain charge neutrality. In the presence of other positively charged impurities, however, such as in Li 1.23 Fe 0.15 Ni 0.15 Mn 0.46 O 2 , 10 where Ni is likely stable as Ni + Li , Fe remains as Fe − Mn . As for the other impurities, Ni + Mn , as an isolated defect, can occur in the form of Ni 0 Mn (i.e., Ni 4+ at the Mn site) at point L; Ni + Li as Ni + Li −η − (E b = 0.55 eV) at points H, H ′ , and D. We note that, if both Ni Li and Ni Mn occur in the material, the charge-compensation mechanism will be different (see more details below).…”

“…6 Experimental studies of doping/co-doping in Li 2 MnO 3 have been carried out by various research groups. 5,[8][9][10][11][12][13][14][15][16] Back in the early 2000s, for example, Lu and Dahn 13 already considered Li[Li 1/3−2x/3 Mn 2/3−x/3 Ni x ]O 2 , which is a Ni-doped Li 2 MnO 3 system. Recent investigations of doped Li 2 MnO 3 materials focused more on understanding the electrochemical activity associated with oxygen redox processes.…”

The application of synchrotron X-ray techniques to the study of rechargeable batteries

“…The details of the redox reaction mechanism in Li-rich x Li 2 MnO 3 •(1-x )LiMO 2 cathode is still ambiguous and under intense discussion, although it is generally accepted that the anionic (O 2 − ) redox processes plays an important role. Combing oxygen K-edge and transition metal l -edges soft XAS and in situ hard XAS, the charge compensation mechanism in this system has been extensively investigated [173][174][175][176][177][178] . Typically reversibly shifts between the charged/discharged states are observed for Ni and Co l -edge XAS spectra, indicating that the Ni and Co ions reversibly participate in the charge compensation.…”

Unveiling the Role of Oxygen Vacancy in Li2MnO3 upon Delithiation

“…Extensive efforts have been made to explore the origin and mechanism behind the undesirable performance of Li 2 MnO 3 . − Some research results provide valuable clues for further optimizing the battery performance. ,− In parallel, structural modification − or elemental substitution ,− have been applied to Li 2 MnO 3 to strengthen its structural stability and improve its electrochemical performance. − Thus far, one of the most recognized mechanisms is that the oxidation of the oxygen anion is responsible for the charge compensation in the Li extraction process. , At the same time, oxygen evolution causes the breakage/formation of the Mn–O bond and the layered-to-spinel structural transition . This has been confirmed by the observed oxygen gas release and X-ray diffraction spectra. , …”