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high-energy-density cathodes has been assigned to anion redox reaction via oxygen ions beyond the cationic redox reactions for lithium-and sodium-ion batteries (LIBs and SIBs). [1][2][3] Unfortunately, the oxygen redox reaction generally makes the oxide framework very unstable with phase transitions, resulting in various electrochemical drawbacks such as a very large voltage decay and irreversible capacity for most Li-and Na-based oxygen redox cathodes. [4][5][6] For LIBs, anomalous charge capacities delivered by oxygen redox reactions at 4.5 V (vs Li + /Li) were observed in Li 2 MnO 3 or Li 2 MnO 3 -containing layered oxides upon charging. [7][8][9] However, totally varied discharge curves were observed, which was induced by Mnmigration from the M layer to the A layer in the cathodes. [10,11] For SIBs, Na[Li 1/3 Mn 2/3 ]O 2 exhibiting the oxygen redox reaction was theoretically designed by our group based on the inspiration that redox-inactive Mn 4+ in an octahedral complex is very difficult to be further oxidized to Mn 5+ for compensating charge imbalance induced by Na-extraction in Na[Li 1/3 Mn 2/3 ]O 2 . [12,13] However, the charge voltage curve did not maintain upon discharging, indicating the severe electrochemical polarization inThe demands for higher energy density of rechargeable batteries have been continuously increasing recently, and cationic redox based current cathodes have little scope to further increase energy density since they already exhibit near-theoretical specific capacities. In this regard, oxygen redox (OR) reactions have emerged as a promising breakthrough for sodium-ion battery (SIB) cathodes. Most OR-based layered oxides suffer from drastic hystereticoxygen capacities upon discharging after the first charging. In contrast, stable and nonhysteretic oxygen capacities are herein enabled via Al 3+ incorporation into Li-excess Na layered oxide (NLMO). By combining experimental work and first-principles calculations, it is found that there is an additional stable phase during the oxygen redox for Al incorporated NLMO in comparison with bare NLMO, which is a critical factor in extending and stabilizing the discharge capacity in thermodynamics. In addition, the additional redoxinactive Al 3+ leads to heterogeneous oxygen redox rather than homogeneous, which results in stabilization of the oxide framework with sensitively control of the oxygen participation upon cycling.

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