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O3-type layered transition metal oxides have shown great promise as high-capacity cathode materials for sodium-ion batteries in large-scale energy storage, due to their low cost and the abundance of sodium resources. However, the limited interlayer spacing and the unstable structure of the O3 phase result in inferior cycling stability and poor rate capability, which could even hinder their practical application process. Hereby, we present that doping with nonelectrochemically active Al in NaAl x (Ni 0.5 Mn 0.5 ) 1−x O 2 (x = 0, 0.02, 0.06, 0.1) can effectively alleviate these issues. Among these materials, materials with x = 0.02 exhibited the best electrochemical behavior with improved capacity and better cycling property than other materials. Specifically, the discharge capacity of a 2 mol % Al-doped material possesses 63.2% capacity retention after 200 cycles at a current density of 240 mA g −1 , which is 21.4% higher than that in NaNi 0.5 Mn 0.5 O 2 . In addition, a 2 mol % Al-doped electrode also shows outstanding rate capability and delivers 90 mAh g −1 at a high rate of 480 mA g −1 , compared to only 67 mAh g −1 for that of the pristine one. X-ray diffraction (XRD), cyclic voltammetry (CV), and galvanostatic intermittent titration technique (GITT) analysis elucidated that the introduced Al dopant can effectively improve the structural stability and promote kinetics of Na + diffusion mobility. Therefore, the strategy of doping inactive aluminum elements for optimizing the electrochemical performance of NaNi 0.5 Mn 0.5 O 2 was verified, which could also open an avenue for the design of other O3-type sodium cathode materials.

Vanadium bronzes have been well-demonstrated as promising cathode materials for aqueous zinc-ion batteries. However, conventional single-ion pre-intercalated V2O5 nearly reached its energy/power ceiling due to the nature of micro/electronic structures and unfavourable phase transition during Zn2+ storage processes. Here, a simple and universal in-situ anodic oxidation method of quasi-layered CaV4O9 in a tailored electrolyte was developed to introduce dual ions (Ca2+ and Zn2+) into bilayer δ-V2O5 frameworks forming crystallographic ultra-thin vanadium bronzes, Ca0.12Zn0.12V2O5·nH2O. The materials deliver transcendental maximum energy and power densities of 366 W h kg−1 (478 mA h g−1 @ 0.2 A g−1) and 6627 W kg−1 (245 mA h g−1 @ 10 A g−1), respectively, and the long cycling stability with a high specific capacity up to 205 mA h g−1 after 3000 cycles at 10 A g−1. The synergistic contributions of dual ions and Ca2+ electrolyte additives on battery performances were systematically investigated by multiple in-/ex-situ characterisations to reveal reversible structural/chemical evolutions and enhanced electrochemical kinetics, highlighting the significance of electrolyte-governed conversion reaction process. Through the computational approach, reinforced “pillar” effects, charge screening effects and regulated electronic structures derived from pre-intercalated dual ions were elucidated for contributing to boosted charge storage properties.