High-Rate Performance of Ultra-Thin Li-Nb-O Thin Films as an Anode for Li-ion Micro-Battery Applications

Abstract

Research and development in Li-ion micro-batteries are focusing on improving their performance, energy density, and cost-effectiveness. These batteries continue to be an area of interest for applications where traditional battery technologies may not be as suitable due to size and weight constraints. In the present work, we report on the electrochemical properties, Li-ion dynamics, various contributions to charge storage, and the ability to glow a light-emitting diode (LED) using Li-Nb-O thin film electrodes deposited via the RF magnetron sputtering technique. X-ray diffraction and Raman spectra analysis identified mixed phases of the thin film of tetragonal Nb₂O₅ and monoclinic LiNb₃O₈, both phases displaying the Nb⁵⁺ oxidation state, as verified by X-ray photoelectron spectroscopy. The cyclic voltammogram and dQ/dV plots demonstrated the two-electron transfers from each phase of the film and the kinetic property of the mixed phase is significantly contributed by both intercalation and pseudocapacitance behavior. The Li-Nb-O ultra-thin film of 19 nm delivers an initial discharge capacity of 9.9 µAh/cm² at a current density of 20 µA/cm² and attained capacity retention of 75.75% after 300 cycles, indicating improved lithium storage. Additionally, impedance measurements are conducted to assess the reduction in charge transfer resistance before and after cycling, and to determine the Li-ion diffusion coefficient, which ranged from 10⁻¹⁷ to 10⁻²⁰ cm²/s in the thin film. Thus, the Li-Nb-O thin films can be suitable as a negative electrode in all-solid thin film micro-batteries applications.