Improved electrochemical performance and chemical stability of thin-film lithium phosphorus oxynitride electrolyte by appropriate fluorine plasma treatment

Abstract

Fluorine plasma treatment is proposed to incorporate fluorine into thin-film lithium phosphorus oxynitride (LiPON@F) electrolyte and its effects on the electrolyte performance and stability are also investigated. Due to strong reactivity of fluorine plasma, fluorine can be easily incorporated into LiPON with negligible effects on its morphologies and amorphousness by appropriate plasma treatment. The LiPON@F electrolyte film displays better performance than the LiPON one mainly in terms of its higher ionic conductivity (σi ∼ 1.0 × 10−6 S cm−1 vs. 7.7 × 10−7 S cm−1), lower activation energy (EA ∼ 0.39 eV vs. 0.46 eV) and larger electrochemically stable window (ESW ∼ 4.2 V vs. 3.9 V). Moreover, the LiPON@F electrolyte film also presents superior chemical stability than the LiPON one (σi degradation after exposure to 50%RH humidity for 120 h ∼ 14.5% vs. 35.4%). Due to strong electronegativity and reactivity of the fluorine plasma, fluorine incorporation passivates defective bonds in the film and breaks the bridging bonds in the phosphate network. These facilitate the Li+ migration and enhance the capability against the moisture, thus improving both the electrochemical performance and chemical stability of the electrolyte films.