Comprehensive X‑ray Photoelectron Spectroscopy Study of the Conversion Reaction Mechanism of CuO in Lithiated Thin Film Electrodes

The course of the conversion reaction during the electrochemical insertion/deinsertion of lithium in CuO thin film electrodes was surveyed by cyclic voltammetry (CV) and X-ray photoelectron spectroscopy (XPS). The electrochemical processes were studied through the comprehensive acquisition and interpretation of XPS and Auger spectra (Cu 2p, O 1s, Cu LMM) recorded at different stages of the first cycle of a Li/CuO cell. The reduction process consisting of three main steps leads successively to Cu⁺ and Cu⁰ and involves a Li₂O₂ peroxide type phase as an intermediate, whereas Li₂O is the main lithiated oxide at the end of the discharge. Only the two last steps appear reversible in charge. No evidence of Cu²⁺ was found at the end of the charge at 3.5 V/Li⁺/Li, showing the irreversibility of the first step in our experimental conditions. Complementary XPS depth profile analyses were performed to check the evolution of the active material composition over the thickness of the electrode

Thorough Characterization of Sputtered CuO Thin Films Used as Conversion Material Electrodes for Lithium Batteries

CuO thin films were prepared by radio frequency magnetron sputtering using a copper target in a (Ar + O₂) reactive mixture. Different sputtering parameters were varied including oxygen flow rate, total pressure, target-substrate distance, substrate temperature and target orientation. As expected, the thin film chemical composition is strongly dependent on the oxygen flow rate. CuO thin films having a good electronic conductivity (9.3 × 10^–1 S·cm^–1) were obtained with an oxygen concentration of 12%. The texture and the columnar growth are amplified when the target is tilted. Preliminary electrochemical results highlight that CuO thin film performances in lithium systems are tightly related to their morphology and structure