Synthesis, structure, and electrochemical behaviour of O3-type NaNi1/3Mn1/3Al1/3O2

Abstract

O3-type layered oxides are being actively investigated as potential positive electrodes for Na-ion batteries due to their high specific capacity. In this work, the role of synthesis conditions on the phase formation in NaNi<inf>1/3</inf>Mn<inf>1/3</inf>Al<inf>1/3</inf>O<inf>2</inf> (NMA111) sample was investigated, and an O3-type phase (R3¯m), along with a minor β-phase (Pn2<inf>1</inf>a), was obtained in the pellet (covered with a sacrificial powder) heated at 850 °C. NMA111 exhibited a mixed conducting behaviour at room temperature, with ionic and electronic conductivities estimated to be ∼5.82 × 10−6 S cm−1 and ∼2.15 × 10−6 S cm−1, respectively. The oxidation states and local structure of Mn and Ni were confirmed by X-ray photoelectron spectroscopy (XPS) and X-ray absorption spectroscopy studies. The electrochemical behaviour of NMA111 was also investigated using the GCD, CV, GITT, and in-situ EIS techniques. The cathode showed an initial discharge capacity of ∼87 mAh g−1 (which corresponds to 0.33 Na-ions reversible intercalation) at 0.1C in the 2.0 to 4.0 V range, and the voltage profile suggested a solid-solution type insert mechanism. A discharged capacity of 70 mAh g−1 at 2C (∼80 % of the initial capacity at 0.1C), and a capacity retention of 70 % after 100 cycles at 0.3C were obtained in the NMA111 cathode. The ex-situ XPS measurements confirmed that the Ni2+/3+ redox couple is responsible for the charge compensation in NMA111 during the charge-discharge process. © 2025 Elsevier B.V., All rights reserved.