image: Reversible anionic-redox and solid-solution chemistry are proposed to address the high-voltage structural instability in practical O3-type sodium layered oxide cathodes. The detrimental P3→O1 phase transition above 4.1 V is completely eliminated, achieving near-zero lattice strain. The as-prepared material exhibits superior electrochemical reversibility at a high voltage of 4.3 V, excellent rate capability, and robust air stability.
Credit: ©Science China Press
In this study, the researchers designed a low-cost O3-type cathode material FMT using earth-abundant elements, achieving remarkable performance improvements. Fe, Mg, and Ti work synergistically to establish an efficient regulation system. Fe replaces nickel and manganese for charge compensation and suppresses structural collapse at high voltage. Mg forms a Na–O–Mg configuration that activates reversible oxygen redox. Ti stabilizes lattice oxygen through strong Ti–O covalent bonds, suppresses complex phase transitions, and promotes solid-solution reactions.
Using this synergistic design, the team addressed the critical challenges facing conventional O3-type cathodes. The strategy realizes highly reversible oxygen redox, suppresses oxygen loss and cathode degradation, and eliminates the detrimental P3→O1 phase transition, ensuring stable performance above 4.1 V. The resulting material also shows near-zero lattice strain and fast Na+ diffusion. Compared with the pristine cathode NaNi0.5Mn0.5O2, FMT exhibits superior cycling stability, rate capability, and air stability.
This breakthrough overcomes key bottlenecks hindering high-voltage O3-type layered oxides and establishes a new paradigm for cathode design.
As Prof. ZHANG Xian-Ming noted, “This study supports the development of high-energy-density, long-life, and scalable sodium-ion batteries. It will accelerate their industrial application in large-scale energy storage and promote the high-quality development of the new energy industry.”