Molecular Layer Deposition for Applications in Lithium-Ion Batteries

Tuesday, 3 October 2017: 09:00
Chesapeake L (Gaylord National Resort and Convention Center)
K. Van de Kerckhove, F. Mattelaer, J. Dendooven, and C. Detavernier (Ghent University)
Molecular layer deposition (MLD) of hybrid organic-inorganic thin films called titanicones, vanadicones, tincones, and alucones was investigated for electrode and solid electrolyte applications in lithium-ion batteries.

The titanicone, vanadicone and tincone films were studied as electrode materials, both as anodes and cathodes. Novel MLD processes were developed for these materials and were based on an alkylamine metal precursor (TDMAT, TEMAV, TDMASn) and glycerol (GL) as the organic reactant. Linear and self-limited growth could be achieved for these metalcones in a broad temperature range with temperature-dependant growth rates ranging from 0.2 to 1.3 Å/cycle. Film growth was studied in situ with spectroscopic ellipsometry (SE) and infrared spectroscopy (FTIR). The as-deposited films appeared to be electrochemically inactive in all cases. A post-deposition heat treatment up to 500°C in either inert (helium) or oxidizing (air) atmosphere was able to electrochemically activate the films. X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) measurements showed that all carbon was removed during calcination in air and that the films crystallized. However, annealing in inert atmosphere conserved the carbon content of the film and thus the films remained amorphous. The performance with increasing charging and discharging rate, and cyclability of the heat-treated MLD electrodes was tested against their respective metal oxide references. The He-annealed metalcones emerged from these tests as the best performing electrodes at higher rates (left and middle figures) and with improved capacity retention and stability during repeated charging and discharging.

The transformation of alucone films, deposited with the TMA and ethylene glycol (EG) or GL process, into porous aluminium oxide was examined. Porous, non-conducting materials are interesting for lithium-ion battery research since they may serve as the matrix template for solid composite electrolytes. Calcination in air and water etching proved to be the most successful methods. For the calcination treatment, a clear relation was found between the ramp rate during both heating and cooling and the resulting porosity of the film (right figure). The aging behaviour of the films in ambient atmosphere was also investigated with FTIR and showed that the films deposited with EG decompose in a matter of only a few hours, as opposed to those deposited with GL.