Insight into electrochemical processes governing the work operation of Na0.67MnO2, Na 0.67 Mn 1-y Li y O 2 and Na 0.67 Mn 1-y Mg y O 2-cathode materials for sodium-ion batteries

Na 0.67 Mn 1- y Li y O 2 and Na 0.67 Mn 1- y Mg y O 2 cathode materials were studied in terms of their possible use in Na-ion batteries. Research on the crystal and electronic structure and their evolution under the influence of partial substitution of manganese with lithium or magnesium were undertaken. Electronic structure calculations for ordered NaMnO2 as well as disordered Na 0.67 Mn 1- y Li y O 2 and Na 0.67 Mn 1- y Mg y O 2 systems proved to be helpful in explaining the anomalous discharge curve for Na 0.67 Mn 1- y Li y O 2 cycled in 1.5-4.4 V and participation of oxygen redox reaction. These investigations were combined with X-ray absorption spectroscopy, Raman and FTIR spectroscopy measurements. Finally, the electrochemical properties of the investigated materials were studied in two voltage ranges: 1.5-4.0 V and 1.5-4.4 V in order to verify the participation of oxygen in redox processes. Xray absorption spectroscopy at oxygen K-edge confirms contribution of oxygen in reversible redox processes for cathode materials with extended electrochemical capacity.