P2–Na2/3Mg1/4Mn7/12Co1/6O2 cathode material based on oxygen redox activity with improved first-cycle voltage hysteresis.

The recent report of P2–Na 2/3 Mg 0.28 Mn 0.72 O 2 (P2-NMM) demonstrated the possibility of utilizing the oxygen redox couple in a layered oxide cathode without the need for alkali ions or vacancies in the transition metal layer. In this work, we report the synthesis of a new P2-type compound, Na 2/3 Mg 1/4 Mn 7/12 Co 1/6 O 2 (P2-NMMC), which exhibits reversible specific capacities as high as 173 mAh g−1 and an improvement of the first cycle voltage hysteresis over P2-NMM. The material was characterised using a combination of ex-situ and operando techniques including X-ray diffraction (XRD), differential electrochemical mass spectrometry (DEMS) and X-ray spectroscopy (XAS) to identify potential sources for this improvement. • P2-NMMC exhibits specific capacities of ≈170 mAh g−1 after 40 cycles. • P2-NMMC has a lower voltage hysteresis (≈0.5 V) than P2-NMM. • Oxygen redox reaction is studied using various ex-situ and operando techniques. [ABSTRACT FROM AUTHOR]