Ab initio prediction of two-dimensional Si₃C enabling high specific capacity as an anode material for Li/Na/K-ion batteries

Anode materials that possess similar electronic structures but larger lattice parameters in comparison with graphene usually show higher theoretical specific capacities for Li/Na/K-ion batteries. Herein, density functional theory (DFT) calculations are applied to evaluate the working performances of a two-dimensional Si₃C monolayer with larger bond lengths than graphene. The negative adsorption energies of Li/Na/K atoms on the surface of the Si₃C monolayer avoid the appearance of dendrites. With the intercalation of Li/Na/K atoms, the Si₃C monolayer exhibits a puckered structure instead of its initial planar structure, lowering the diffusion energy barrier of Li/Na/K atoms. The theoretical specific capacities for Li, Na and K-ion batteries are estimated to be as high as 1394, 1115 and 836 mA h g^-1, corresponding to the stoichiometries of Li₅Si₃C, Na₄Si₃C and K₃Si₃C, respectively. The average open circuit voltages (OCVs) for Li/Na/K-ion batteries are 0.58 V, 0.50 V and 0.71 V, respectively. The density of states (DOS) calculation reveals that the Si₃C monolayer is semimetallic and its electronic conductivity can be enhanced by the intercalation of alkali metal atoms. In Li, Na and K-ion batteries, it is found that the maximum variations of lattice parameters of the Si₃C monolayer are 3.54%, 2.69% and 2.24%, respectively. All the desirable properties indicate that the Si₃C monolayer is a promising anode material for Li/Na/K-ion batteries. It also suggests that silicene doped with moderate carbon or some other elements is a potential anode material for alkali metal-based batteries.