Ca-doped NaV6O15 film electrodes as high-performance cathodes for sodium-ion batteries

Abstract

The Ca-doped NaV6O15 films have been prepared on indium-doped tin oxide (ITO) conductive glasses using a low-temperature liquid-phase deposition method. The crystal structure, morphology, and structural information of the Ca-doped NaV6O15 films were systematically studied by X-ray diffraction, scanning electron microscopy and infrared spectroscopy. X-ray photoelectron spectroscopy revealed that the Ca-doped NaV6O15 had a lower ratio of V5+/V4+, which was the compensation for doped Ca2+. Electrochemical properties of films were measured by cyclic voltammetry, electrochemical impedance spectroscopy and galvanostatic charge/discharge tests. The results proved the doped Ca2+ obviously improved electrochemical performance, which exhibited quicker diffusion process, higher specific capacity, and longer lifespan. The Ca-doped NaV6O15 films showed a high discharge capacity of 237.476 mA h m−2 at 1C rate, which was larger than 96.719 mA h m−2 of the pure NaV6O15 films. The capacity retention reached to 84.72 % at 0.5C rate after 100 cycles, the excellent cyclic ability was attributed to the doped Ca2+ with strong electronegativity stabilizing the structure. This work presents a great potential approach that explores high-performance cathodes for sodium-ion batteries.