Fluorine-substituted O3-type NaNi0.4Mn0.25Ti0.3Co0.05O2-xFx cathode with improved rate capability and cyclic stability for sodium-ion storage at high voltage

O3-type NaNiO2-based cathode materials undergo irreversible phase transition and serious capacity decay at high voltage above 4.0 V in sodium-ion batteries. To address these challenges, effects of F-substitution on the structure and electrochemical performance of NaNi0.4Mn0.25Ti0.3Co0.05O2 are investigated in this article. The F-substitution leads to expanding of interlayer, which can enhance the mobility of Na+. NaNi0.4Mn0.25Ti0.3Co0.05O1.92F0.08 (NMTC-F-0.08) with the optimal F-substitution degree exhibits much improved rate capability and cyclic stability. It delivers reversible capacities of 177 and 97 mAh g(-1) at 0.05 and 5 C within 2.0-4.4 V, respectively. Galvanostatic intermittent titration technique verifies faster kinetics of Na+ diffusion in NMTC-F-0.08. And in-situ XRD investigation reveals the phase evolution of NMTC-F-0.08, indicating enhanced structural stability results from F-substitution. This study may shed light on the development of high performance cathode materials for sodium-ion storage at high voltage. (C) 2021 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

In this study, the effects of F-substitution on the structure and electrochemical performance of NaNi0.4Mn0.25Ti0.3Co0.05O2 were investigated. It was found that optimal F-substitution led to improved rate capability and stability, as well as enhanced Na+ mobility. Additionally, in-situ XRD investigation revealed enhanced structural stability resulting from F-substitution.