Exploring the Impact of Lanthanum on Sodium Manganese Oxide Cathodes: Insight into Electrochemical Performance

Abstract

This investigation focuses on nominally La-doped Na_0.67MnO₂, exploring its structural, electrochemical, and battery characteristics for Na-ion batteries. X-ray diffraction analysis reveals formation of composite materials containing three distinct phases: P2-Na_0.67MnO₂, NaMn₈O₁₆, and LaMnO₃. The bond structures of the powders undergo scrutiny through Fourier-transform infrared and Raman analyses, revealing dependencies on the NaO, MnO, and LaO structures. X-ray photoelectron spectroscopy and energy-dispersive X-ray dot mapping analyses show that the La ions are unevenly dispersed within the samples, exhibiting a valence state of 3+. Half-cell tests unveil similarities in redox peaks between the cyclic voltammetry analysis of La-doped samples and P2-type Na_0.67MnO₂, with a reduction in peak intensities as La content increases. Electrochemical impedance spectroscopy model analysis indicates direct influences of La content on the half-cell's resistive elements values. The synergistic effect of composite material with multiple phases yields promising battery performances for both half and full cells. The highest initial capacity value of 208.7 mAh g⁻¹, with a 57% capacity fade, among others, is observed, and it diminishes with increasing La content. Full cells are constructed using an electrochemically presodiated hard carbon anode, yielding a promising capacity value of 184.5 mAh g⁻¹ for sodium-ion battery studies.