The substitution of critical raw materials, such as Ni, in layered oxide cathode materials offers a promising pathway to enhance the cycling stability and mean voltage of sodium-ion batteries. Beyond the general entropy enhancement, the precise selection of redox-active elements and structurally stabilizing dopants critically influences the cycling performance and stability of the P2-type layered oxide cathode materials investigated in this study.
Through material screenings, a variety of metal stoichiometries were achieved using a one-step reaction process, which resembles the planned precipitation scale-up technique in terms of the targeted precursor chemistry.
A systematic characterization by XRD and ICP-OES reveals structural properties, while SEM analytics provides insights into the morphology. Half-cell cycling experiments demonstrate a significantly improved cycle stability and an increased mean voltage of the doped layered oxide materials.
By comparing the stoichiometry to the analytical results and the electrochemical data, we can explain the stabilizing effects of the doping substituents and the specific capacity design.
In summary, this work highlights the influence of targeted doping with abundant elements in P2-type layered oxides to achieve enhanced cycling stability and voltage increase in sodium-ion batteries, evidenced by the systematic material screening results.

ACKNOWLEDMENT:
This work was supported by the German Federal Ministry of Education and Research (BMBF) in the project Entise (03XP0579D).

REFERENCES:
1) Pfeiffer, L. F. et al., Layered P2-NaxMn3/4Ni1/4O2 Cathode Materials For Sodium-Ion Batteries: Synthesis, Electrochemistry and Influence of Ambient Storage, Front. Energy Res. 10, 305; 10.3389/fenrg.2022.910842 (2022).

2) J. Zhan J., J. Huang, Z. Li, J. Yuan, S. Dou, H. Liu C. Wu, Air-Stable High-Entropy Layered Oxide Cathode with Enhanced Cycling Stability for Sodium-Ion Batteries, Nano Lett. 24, 32, 9793–9800; 10.1021/acs.nanolett.4c00968 (2024).

3) J. Wang, S. L. Dreyer, K. Wang, Z. Ding, T. Diemant, G. Karkera, Y. Ma, A. Sarkar, B. Zhou, M. V. Gorbunov, et al. P2-type layered high-entropy oxides as sodium-ion cathode materials, Mater. Futures 1, 035104; 10.1088/2752-5724/ac8ab9 (2022).