fig16

Figure 16. (A) In-situ SHINERS spectra recorded during initial two cycles with reversible generation and migration of peroxo O^--O^- at high voltage^[87]. (B) X-band in-situ EPR spectra of Li₂Ru_0.75Sn_0.25O₃ during the initial charge between 2.0 and 4.6 V. Ru⁴⁺/⁵⁺ charge compensation occurs in the low-voltage plateau area and the reductive coupling of Ru and oxygen occurs in the first half of the high-voltage plateau with the oxidation process of pure O^2- in the second half^[203]. (C) Cr K-edge XAS spectra (top) of Li_1.2Mn_0.2Ti_0.4Cr_0.2O₂ in pristine (black solid line), 4.8 V-charged (red solid line) and 1.5 V-discharged states (gray solid line). LiCrO₂, CrO₂ and CrO₃ standard spectra are plotted as dashed lines. Fitted Cr K-edge EXAFS spectra (bottom) of Li_1.2Mn_0.2Ti_0.4Cr_0.2O₂ in pristine and 4.8 V-charged states. Peaks at ~1.0, ~1.5 and ~2.5 Å correspond to the tetrahedral Cr-O, octahedral Cr-O and Cr-TM coordinations, respectively^[109]. (D) Solid-state ¹⁷O MAS NMR spectra showing the molecular O₂ trapped in the bulk of the cathode particles in the state of full charge^[41]. (E) Soft X-ray RIXS data proves that oxygen redox occurs when Li_1.2Ni_0.13Co_0.13Mn_0.54O₂ is charged to 4.8 V^[205]. (F) O 1s HAX-PES spectra (left) of Li[Li_0.25Ni_0.20Mn_0.55]O_1.93 electrodes for the 1st cycle. The sampling points correspond to the image on the right with the intensity ratio of [O^-]/[O^- + O^2-]^[207]. SHINERS: Shell-isolated nanoparticle-enhanced Raman spectroscopy; EPR: electron paramagnetic resonance; XAS: X-ray absorption spectroscopy; EXAFS: extended X-ray absorption fine structure; NMR: nuclear magnetic resonance; RIXS: resonant inelastic X-ray scattering; HAX-PES: hard X-ray photoelectron spectroscopy.