Molecular layer deposition of “vanadicone”, a vanadium-based hybrid material, as an electrode for lithium-ion batteries

Abstract

Molecular layer deposition (MLD) of hybrid organic–inorganic thin films called “vanadicones” was investigated using tetrakisethylmethylaminovanadium (TEMAV) as the metal precursor and glycerol (GL) or ethylene glycol (EG) as the organic reactant. Linear and continued growth could only be achieved with GL as the organic reactant. The TEMAV/GL process displayed self-limiting reactions for both precursor and reactant pulses in the temperature range from 80 °C to 180 °C, with growth rates of 1.2 to 0.5 Å per cycle, respectively. Infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) revealed the hybrid nature of the films. From X-ray reflectivity, the density was estimated at 2.6 g cm⁻³. A series of 21 nm vanadicone films were subjected to annealing under oxidizing (air) or inert (He) atmospheres at 500 °C. During annealing in air, the film crystallized to the V₂O₅ phase and all carbon was removed from the film. The films annealed in helium remained amorphous and retained most of their carbon content. Electrochemical measurements revealed lithium-ion activity during cyclic voltammetry in all treated films, while the as deposited film was inactive. In the 2.9 to 3.5 V vs. Li⁺/Li potential region, no improvement over the V₂O₅ reference was observed. However, the helium annealed samples outperformed V₂O₅ in terms of capacity, rate performance and cyclability when charged and discharged in the 1.0 to 3.5 V vs. Li⁺/Li region. This result enables the application of V_xO_y-based hybrid electrodes in a wider potential range without sacrificing the stability and performance.