Mg Substitution Induced TM/Vacancy Disordering and Enhanced Structural Stability in Layered Oxide Cathode Materials
Luyao Wang, Chu Zhang, Lu Yang, Shuwei Li, Hang Chu, Guangmao Li, Ying Meng, Haoyu Zhuang, Yurui Gao, Zhiwei Hu, Jin‐Ming Chen, Shu‐Chih Haw, Cheng‐Wei Kao, Ting‐Shan Chan, Xi Shen, Zhaoxiang Wang, Richeng Yu
Abstract
Anionic redox is an effective way to increase the capacity of the cathode materials. Na 2 Mn 3 O 7 [Na 4/7 [Mn 6/7 □ 1/7 ]O 2, □ for the transition metal (TM) vacancies] with native and ordered TM vacancies can conduct a reversible oxygen redox and be a promising high-energy cathode material for sodium-ion batteries (SIBs). However, its phase transition at low potentials (∼1.5 V vs Na + /Na) induces potential decays. Herein, magnesium (Mg) is doped on the TM vacancies to form a disordered Mn/Mg/□ arrangement in the TM layer. The Mg substitution suppresses the oxygen oxidation at ∼4.2 V by reducing the number of the Na–O–□ configurations. Meanwhile, this flexible disordering structure inhibits the generation of the dissolvable Mn 2+ ions and mitigates the phase transition at ∼1.6 V. Therefore, the Mg doping improves the structural stability and its cycling performance in 1.5–4.5 V. The disordering arrangement endows Na 0.49 Mn 0.86 Mg 0.06 □ 0.08 O 2 with a higher Na + diffusivity and improved rate performance. Our study reveals that oxygen oxidation is highly dependent on the ordering/disordering arrangements in the cathode materials. This work provides insights into the balance of anionic and cationic redox for enhancing the structural stability and electrochemical performance in the SIBs.