Abstract
The revival of the Na‐ion battery concept has prompted intense research activities toward new sustainable Na‐based insertion compounds and their implementation in full Na‐ion cells. Efforts are parted between Na‐based polyanionic and layered compounds. For the latter, there has been a specific focus on Na‐deficient layered phases that show cationic and anionic redox activity similar to a Na0.67Mn0.72Mg0.28O2 phase. Herein, a new alkali‐deficient P2‐Na2/3Mn7/9Zn2/9O2 phase using a more electronegative element (Zn) than Mg is reported. Like its Mg counterpart, this phase shows anionic redox activity and no O2 release despite evidence of cationic migration. Density functional theory (DFT) calculations show that it is the presence of an oxygen nonbonding state that triggers the anionic redox activity in this material. The phase delivers a reversible capacity of 200 mAh g−1 in Na‐half cells with such a value be reduced to 140 mAh g−1 in full Na‐ion cells which additionally shows capacity decay upon cycling. These findings establish Na‐deficient layered oxides as a promising platform to further explore the underlying science behind O2 release in insertion compounds based on anionic redox activity.