Achieving stable anionic redox chemistry in Li-excess O2-type layered oxide cathode via chemical ion-exchange strategy

Triggering oxygen redox activity has been regarded as a promising strategy to boost the output capacity of cathode materials for Li/Na-ion batteries. However, irreversible loss of lattice oxygen aggravates a structural distortion to a spinel phase, which leads to severe voltage decay and capacity degeneration. Herein, via chemical ion exchange procedure, the sodium within the alkali metal layer of a P2-type oxide precursor has been substituted by Li while the transition metal layer can be well preserved, resulting in the formation of a Li-excess O2-type layered oxide cathode, Li0.66[Li0.12Ni0.15Mn0.73]O2. Through systematic in/ex-situ and surface/bulk characterization (hard X-ray absorption spectroscopy, operando Raman/XRD and differential electrochemical mass spectroscopy, etc.), the redox reversibility and structural stability has been comprehensively demonstrated. Moreover, being evolved from the same sodium-based precursor, a similar O2-type compound generated by electrochemical ion exchange procedure presents severely irreversible behavior on both structural and redox processes. These findings elucidated that the chemical ion exchange strategy can be regarded as an efficient way to design high-capacity cathode candidates possessing stable anionic/cationic redox activities and enhanced structural stability.