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Inthis study, a new ReaxFF reactive force field has been developed todescribe reactions in Ti/O/Cl/H materials. This force field was appliedto etching simulations for titanium metal and titanium dioxide withchlorine and hydrogen chloride gases. The ReaxFF force field parametersare fitted against a quantum mechanical (QM) training set containingstructures and energies related to bond dissociations, angle and dihedraldistortions, and reactions between titanium and chlorine gases aswell as heats of formation of TiClxcrystals.These newly developed Ti–Cl force field parameters were combinedwith a recently developed Ti–O–H force field. ReaxFFaccurately reproduces the QM training set for structures and energeticsof small clusters and TiClxcrystals.In the etching simulations, titanium and titanium dioxide slab modelswith chlorine and hydrogen chloride gases were used in molecular dynamicssimulations. The etching ratio between HCl and Cl2arecompared to experimental results, and satisfactory results are obtained,indicating that this ReaxFF extension provides a useful tool for studyingthe atomistic-scale details of the etching process. [ABSTRACT FROM AUTHOR]

Atomically deposited layers of SiO2 and Al2O3 have been recognized as promising coating materials to buffer the volumetric expansion and capacity retention upon the chemo-mechanical cycling of the nanostructured silicon- (Si-) based electrodes. Furthermore, silica (SiO2) is known as a promising candidate for the anode of next-generation lithium ion batteries (LIBs) due to its superior specific charge capacity and low discharge potential similar to Si anodes. In order to describe Li-transport in mixed silica/alumina/silicon systems we developed a ReaxFF potential for Li-Si-O-Al interactions. Using this potential, a series of hybrid grand canonical Monte Carlo (GCMC) and molecular dynamic (MD) simulations were carried out to probe the lithiation behavior of silica structures. The Li transport through both crystalline and amorphous silica was evaluated using the newly optimized force field. The anisotropic diffusivity of Li in crystalline silica cases is demonstrated. The ReaxFF diffusion study also verifies the transferability of the new force field from crystalline to amorphous phases. Our simulation results indicates the capability of the developed force field to examine the energetics and kinetics of lithiation as well as Li transportation within the crystalline/amorphous silica and alumina phases and provide a fundamental understanding on the lithiation reactions involved in the Si electrodes covered by silica/alumina coating layers.