Monitoring the Local Coordination Evolutions in Li-Rich Cathode Materials via In Situ Raman Spectroscopy

Although consensus has been reached that the lattice oxygen (O2–) could be ultimately oxidized to molecular O2 in lithium-rich cathode materials (LRCMs), monitoring the local coordination evolutions around oxygen in real time is still demanding. Herein, we demonstrate the potential of using in situ Raman spectroscopy to decipher the local environment changes upon de-/lithiation in Li2RuO3. Evolutions of both the Ru–Ru motions and Ru–O vibrations have been captured by in situ Raman tests and interpreted in combination with multimodal characterizations. Uniquely, triggering the anion redox reactions (ARRs) produces a Raman band (∼500 cm–1), which upon careful examination is attributed to the Ru–O2n– (0 < n < 4) coordination and suggested as the indicator of O–O dimerization. Considering its nondestructivity and high sensitivity to lattice vibrations, this work could shed new light on utilizing Raman spectroscopy to investigate the local coordination evolutions in LRCMs and other materials.