Molecular Layer Deposition of Organic–Inorganic Hafnium Oxynitride Hybrid Films for Electrochemical Applications

Abstract

The molecular layer deposition (MLD) method can be used to deposit hybrid organic–inorganic films with precisely defined composition, flexible properties, and conformality on different substrates. In this study, hafnium-based organic–inorganic hybrid polymer films were studied as potential coatings for silicon nanoparticles (SiNPs) used in composite lithium-ion battery (LIB) anodes, an application which requires the film to be both flexible and stable under electrochemical conditions. Hf-hybrid films were successfully deposited by MLD using sequential exposure of the homoleptic tetrakis(dimethylamido) hafnium complex and ethanolamine as the reactants. The self-limiting surface reactions lead to a constant growth per cycle (GPC) of ∼2.0 Å/cycle at 120 °C. Temperature-dependent growth was observed, with the GPC decreasing from ∼2.5 to ∼1.1 Å/per cycle as the temperature was increased from 65 to 145 °C. Scanning transmission electron microscopy and electron energy loss spectroscopy mapping confirm that a thin, dense, and conformal Hf-based MLD layer is deposited on the SiNPs. The presence of expected C–N, C–O, and −CH2 moieties in the MLD films was confirmed by Fourier transform infrared spectroscopy. Hafnium nitride and hafnium oxide bonds within the hybrid thin films were identified by X-ray photoelectron spectroscopy. Characterization results indicated that the deposited hafnium-based organic–inorganic hybrid films contain both metal oxynitride bonds and organic bonds, including C–C, C–O, and C–N. This Hf-based MLD thin film was tested on LIB SiNP composite anodes as an artificial solid–electrolyte interphase, with results showing that the capacity retention increased by about 35% after 110 cycles in a LIB application.