Ti‐Substituted NaNi0.5Mn0.5‐xTixO2 Cathodes with Reversible O3−P3 Phase Transition for High‐Performance Sodium‐Ion Batteries

• Published in: Advanced materials (Weinheim) 2017-05, Vol.29 (19), p.n/a
• Main Authors: Wang, Peng‐Fei, Yao, Hu‐Rong, Liu, Xin‐Yu, Zhang, Jie‐Nan, Gu, Lin, Yu, Xi‐Qian, Yin, Ya‐Xia, Guo, Yu‐Guo
• Format: Article
• Language: English
• Subjects: Cathodes; Electric potential; Electrochemical analysis; electrochemistry; Energy storage; Intercalation; Low cost; Materials science; Modulation; Multiphase; O3−P3; Oxides; phase transition; Phase transitions; Physical properties; Rechargeable batteries; Scanning electron microscopy; Scanning transmission electron microscopy; Sodium-ion batteries; Spectroscopic analysis; Storage batteries; Transmission electron microscopy; X-ray diffraction; X-rays
• ISSN: 0935-9648; 1521-4095
• DOI: 10.1002/adma.201700210

Sodium‐ion batteries (SIBs) have been considered as potential candidates for stationary energy storage because of the low cost and wide availability of Na sources. O3‐type layered oxides have been considered as one of the most promising cathodes for SIBs. However, they commonly show inevitable complicated phase transitions and sluggish kinetics, incurring rapid capacity decline and poor rate capability. Here, a series of sodium‐sufficient O3‐type NaNi0.5Mn0.5‐ x Ti x O2 (0 ≤ x ≤ 0.5) cathodes for SIBs is reported and the mechanisms behind their excellent electrochemical performance are studied in comparison to those of their respective end‐members. The combined analysis of in situ X‐ray diffraction, ex situ X‐ray absorption spectroscopy, and scanning transmission electron microscopy for NaNi0.5Mn0.2Ti0.3O2 reveals that the O3‐type phase transforms reversibly into a P3‐type phase upon Na+ deintercalation/intercalation. The substitution of Ti for Mn enlarges interslab distance and could restrain the unfavorable and irreversible multiphase transformation in the high voltage regions that is usually observed in O3‐type NaNi0.5Mn0.5O2, resulting in improved Na cell performance. This integration of macroscale and atomicscale engineering strategy might open up the modulation of the chemical and physical properties in layered oxides and grasp new insight into the optimal design of high‐performance cathode materials for SIBs. Here, a structure optimization of NaNi0.5Mn0.5O2 through a partial Ti substitution strategy is designed, yielding a series of sodium‐sufficient O3‐NaNi0.5Mn0.5‐xTixO2 (0 ≤ x ≤ 0.5) cathodes for sodium‐ion batteries for the first time. The substitution of Ti for Mn could suppress irreversible multiphase transformation in the high voltage regions that is usually observed in O3‐type NaNi0.5Mn0.5O2 and retain a highly reversible O3−P3 phase transition, resulting in improved Na cell performance.