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

The molecular layer deposition (MLD) method can be usedto deposithybrid organic-inorganic films with precisely defined composition,flexible properties, and conformality on different substrates. Inthis study, hafnium-based organic-inorganic hybrid polymerfilms were studied as potential coatings for silicon nanoparticles(SiNPs) used in composite lithium-ion battery (LIB) anodes, an applicationwhich requires the film to be both flexible and stable under electrochemicalconditions. Hf-hybrid films were successfully deposited by MLD usingsequential exposure of the homoleptic tetrakis-(dimethylamido) hafniumcomplex and ethanolamine as the reactants. The self-limiting surfacereactions lead to a constant growth per cycle (GPC) of similar to 2.0 angstrom/cycle at 120 degrees C. Temperature-dependent growth was observed,with the GPC decreasing from similar to 2.5 to similar to 1.1 angstrom/percycle as the temperature was increased from 65 to 145 degrees C. Scanningtransmission electron microscopy and electron energy loss spectroscopymapping confirm that a thin, dense, and conformal Hf-based MLD layeris deposited on the SiNPs. The presence of expected C-N, C-O,and -CH2 moieties in the MLD films was confirmedby Fourier transform infrared spectroscopy. Hafnium nitride and hafniumoxide bonds within the hybrid thin films were identified by X-rayphotoelectron spectroscopy. Characterization results indicated thatthe deposited hafnium-based organic-inorganic hybrid filmscontain both metal oxynitride bonds and organic bonds, including C-C,C-O, and C-N. This Hf-based MLD thin film was testedon LIB SiNP composite anodes as an artificial solid-electrolyteinterphase, with results showing that the capacity retention increasedbyabout 35% after 110 cycles in a LIB application.

Automated summary

The molecular layer deposition (MLD) method was successfully used to deposit hafnium-based organic-inorganic hybrid polymer films on silicon nanoparticles (SiNPs) for composite lithium-ion battery (LIB) anodes. The deposited films showed flexible and stable properties under electrochemical conditions. The MLD process involved sequential exposure of hafnium complex and ethanolamine reactants, resulting in self-limiting surface reactions and a constant growth per cycle (GPC) of approximately 2.0 angstrom/cycle at 120 degrees C. The characterization results confirmed the presence of metal oxynitride and organic bonds in the deposited films. The testing on LIB SiNP composite anodes showed a 35% increase in capacity retention after 110 cycles.