New Insights into Anionic Redox in P2-Type Oxide Cathodes for Sodium-Ion Batteries
Zhixiong Huang, Kai Li, Junming Cao, Kai-Yang Zhang, Han‐Hao Liu, Jin‐Zhi Guo, Yan Liu, Ting Wang, Dongmei Dai, Xin-Yi Zhang, Hongbo Geng, Xing‐Long Wu
Abstract
Manganese/nickel-based layered transition metal oxides have caught the attention of studies as promising cathodes for sodium-ion batteries (SIBs). It is reported that utilizing both cationic and anionic redox reactions is a promising method for higher energy density cathodes. However, the anionic redox reaction comes at the expense of irreversible oxygen release. Hence, a Li–Mg cosubstituted P2-Na 0.67 Li 0.07 Mg 0.07 Ni 0.28 Mn 0.58 O 2 material with a honeycomb-ordered superstructure was designed. The Ni 3+ /Ni 4+ redox couple and the anionic redox reaction are proven to have a competitive relationship. Density functional theory calculations reveal the effect of O 2p nonbonding states from Li and prove that Mg–O bonds can stabilize the Ni–O e g states. In situ electrochemical impedance spectroscopy measurements and galvanostatic charging/discharging derived d V /d Q, representing resistance changes with time, are obtained to reveal the mechanism of the anionic redox reaction. This study presents the effect and mechanism of the O 2p nonbonding state and Mg–O bonds of manganese/nickel-based layered oxides.