Simulation of Lithium Adsorption in 4H–SiC, Electron Transfer, and Thermodynamic Functions of Si–C–Li Compounds

Abstract

The adsorption, electronic, and thermodynamic properties of the 2 × 2 × 1 and 3 × 3 × 1 supercells of the binary compounds (\({{{\text{A}}}_{n}}{{{\text{B}}}_{m}} = 4{\text{H}}- {\text{SiC}},\) \({{\alpha }}{\kern 1pt} {\text{ - }}{\kern 1pt} {\text{L}}{{{\text{i}}}_{2}}{{{\text{C}}}_{2}},\) \({\text{L}}{{{\text{i}}}_{n}}{\text{S}}{{{\text{i}}}_{m}}\)) of the Si–C–Li system were studied using the density functional theory (DFT). The theoretical capacity of the 4H–SiC hexagonal polytype was found to exceed that of graphite (370 mA h/g) used as an anode material for lithium-ion batteries. The crystalline compounds \({{{\text{A}}}_{n}}{{{\text{B}}}_{m}}\) have electronic conductivity. The DFT calculations used the exchange-correlation functional within the framework of the generalized gradient approximation (GGA PBE). The parameters of the crystal structure, the adsorption energy of the \({\text{L}}{{{\text{i}}}_{{{\text{ads}}}}}\) adatom on the 4H–SiC substrate, the electronic band structure, and the thermodynamic properties of the supercells of \({{{\text{A}}}_{n}}{{{\text{B}}}_{m}}\) compounds were calculated. The thermodynamically favorable position of \({\text{L}}{{{\text{i}}}_{{{\text{ads}}}}}\) and the stable configuration of the 4H–SiC〈Li_ads〉 supercells were determined. The DFT calculations of the enthalpy of formation of \({{{\text{A}}}_{n}}{{{\text{B}}}_{m}}\) compounds in the Si–C–Li ternary system were performed. The calculated characteristics of \({{{\text{A}}}_{n}}{{{\text{B}}}_{m}}\) agree with the experimental data. The equilibrium connodes in the concentration triangle of Si–C–Li were established using the standard thermodynamic potentials of \({{{\text{A}}}_{n}}{{{\text{B}}}_{m}}\) compounds and the changes in energy in solid-phase exchange reactions between these compounds. An isothermal section of the phase diagram of Si–C–Li at 298 K was constructed.