Properties of Rich-Na<sub>e</sub> Effect and Zero-Phase Transition in P2–Na<sub>0.67</sub>(Ni<sub>0.1</sub>Mn<sub>0.8</sub>Fe<sub>0.1</sub>)<sub>1–<i>x</i></sub>Mg<sub><i>x</i></sub>O<sub>2</sub> Cathodes for Rapid and Stable Sodium Storage
Rui Huang, Shaohua Luo, Pengyu Li, Qi Sun, Guodong Hao, Jie Feng, Lixiong Qian, Shengxue Yan, Jing Guo
Abstract
Mn-rich ternary cathodes are highly regarded as a potential option for sodium-ion batteries (SIBs) due to their low cost and high theoretical capacity. Nonetheless, cycling stability was hindered by the occurrence of high-voltage phase transitions. In this work, Na 0.67 (Ni 0.1 Mn 0.8 Fe 0.1 ) 1– x Mg x O 2 (NaNMF-Mg x ) cathode materials with high-voltage zero-phase transitions property were successfully synthesized. Amazingly, it was found that there was a valuable strengthening in the occupancy of stabler Na e sites by employing the Mg-doping strategy; and the calculation highlighted excellent structural stability and conductivity of NaNMF-Mg0.04, which has the lowest thermodynamic formation energy and a narrow band gap. The combination of theory and experiment demonstrated the underlying mechanisms of Mg substitution. Especially, Mg doping had the potential to regulate Na e /Na f ratio, and the ratio of NaNMF-Mg0.04 reached the maximum, indicating its most remarkable “rich-Na e ” effect. Moreover, ex-situ XRD and ADF-STEM certified that NaNMF-Mg0.04 cathode maintained an intact P2 phase structure during high-voltage charging process. The “rich-Na e ” and “zero-phase transitions” effects enabled NaNMF-Mg0.04 cathode to express remarkable initial capacitance (119.5 mAh g –1, 0.1 C), stability (80.0% over 200 cycles), and energy density (356.5 Wh kg –1 ). This unique mechanism provided fresh insights into revisiting the relationship between structure and performance and might open up a new idea for designing novel Mn-rich ternary cathodes with zero-phase transitions property in the future.