In situ Raman spectroscopy reveals the mechanism of titanium substitution in P2-Na2/3Ni1/3Mn2/3O2: Cathode materials for sodium batteries

Layered P2-Na(2/3)Ni(1/3M)n(2/3)O(2) is a promising cathode material. It exhibits a high capacity and suitable operating voltage and undergoes a phase transition from P2 to O2 during charge/discharge. Researchers have used Ti substitution to improve the cathode, yet the chemical principles that underpin elemental substitution and functional improvement remain unclear. To clarify these principles, we used in situ Raman spectroscopy to monitor chemical changes in P2-Na2/3Ni1/3Mn1/3Ti1/3O2 and P2-Na(2/3)Ni(1/3M)n(2/3)O(2) during charge/discharge. Based on the change in the A(1g) and E-g peaks during charge/discharge, we concluded that Ti substitution compressed the transition metal layer and expanded the planar oxygen layer in the unit cell. Titanium stabilized the P2 phase structure, which improved the cycling stability of P2-NaNMT. Our results provide clear theoretical support for future research on modifying electrodes by elemental substitution. (C) 2020 Science Press and Dalian Institute of Chemical Physics, Chinese Academy of Sciences. Published by ELSEVIER B.V. and Science Press. All rights reserved.

Automated summary

Layered P2-Na(2/3)Ni(1/3M)n(2/3)O(2) is a promising cathode material with high capacity and suitable operating voltage. Ti substitution has been found to improve the cathode and enhance cycling stability by compressing the transition metal layer and expanding the planar oxygen layer in the unit cell. Our results offer theoretical support for future research on modifying electrodes through elemental substitution.