Understanding Oxygen Redox in Cu-Doped P2-Na0.67Mn0.8Fe0.1Co0.1O2 Cathode Materials for Na-Ion Batteries

• Published in: Journal of the Electrochemical Society 2018, Vol.165 (16), p.A3854-A3861
• Main Authors: Li, Ling, Wang, Huibo, Han, Wenze, Guo, Hao, Hoser, Andreas, Chai, Yujun, Liu, Xiangfeng
• Format: Article
• Language: English
• ISSN: 1945-7111
• DOI: 10.1149/2.0691816jes

Oxygen redox chemistry has attracted much attention as an extra charge compensation mechanism to attain the high specific capacity for Na-ion battery cathodes. But how to modulate the crystal and electronic structure to achieve a simultaneous enhancement of anionic and cationic redox is still a big challenge. Herein, the positive effect of Cu doping on both the anionic and cationic redox in P2-Na0.67Mn0.8Fe0.1Co0.1O2 has been reported for the first time, and the roles of Cu have been unveiled. Cu doping increases the lattice parameters a and c as well as enlarges the interslab spacing and Na-O bond length, which reduces the electrostatic attraction between Na and O, and subsequently enhances Na+ diffusion coefficient and rate capability. Moreover, Cu doping decreases Mn3+/Mn4+ ratio and alleviates Jahn-Teller distortion, which benefits to the layered structure stability. More importantly, Cu doping reduces the slab thickness of TMO2 and TM-O/O-O bond length as well as mitigates the lattice volume change and the phase transition, which improves the structure stability and the cycling stability. The strengthened TM-O/O-O bonding energy also suppresses O2 release and improves the reversibility of oxygen redox, which has been further confirmed by differential scanning calorimeter and ex-situ X-ray photoelectron spectroscopy.