Aluminum functionalized silicene: a potential anode material for alkali metal ion batteries

We have investigated the possibility of using aluminum functionalized silicene trilayers (ABC-Si$_4$Al$_2$) as an anode material for alkali metal ion batteries (AMIBs). First, we studied the thermodynamic stability of ABC-Si$_4$Al$_2$ using ab-initio molecular dynamics simulations, showing that this material remains stable up to 600 K. Then, we explored the properties of alkali metal atoms (Li, Na, K) adsorption in ABC-Si$_4$Al$_2$, finding several available sites with high adsorption energies. Moreover, we computed the diffusion properties of those atoms along high-symmetry paths using the nudged elastic band method. The results indicated diffusion barriers as low as those in graphite, especially for Na (0.32 eV) and K (0.22 eV), which allows those ions to migrate easily on the material's surface. Our studies also revealed that the full loaded Li$_4$Si$_4$Al$_2$, Na$_2$Si$_4$Al$_2$, and K$_2$Si$_4$Al$_2$ systems provide low open-circuit voltage, ranging from 0.14 to 0.49 V, and large theoretical capacity of 645 mAh/g for Li- and 322 mAh/g for Na- and K-ion batteries, values that are close to the ones in other anode materials, such as graphite, TiO$_2$, and silicene-based systems. Those results indicate that aluminum functionalized few-layer silicene is a promising material for AMIBs anodes, particularly for Na- and K-ion batteries.