G-Si x C y as an anode material for potassium-ion batteries insight from first principles

Highlights: • The theoretic capacity of g-SiC₅ and g-Si₂C₄ are 304.1 mA h/g and 128.6 mA h/g for KIB. • Low energy barrier of potassium ions diffused on the 2D-siligraphene. • Siligraphene show excellent electrical conductivity. Designing new electrode materials with higher capacity is the key to improve energy density of potassium ion batteries. It is well known that graphene has a low capacity but with high stability, while silicene just opposite. Inspired by this, first-principles calculations were used to evaluate whether siligraphene, the combination of monolayer silicon and monolayer carbon is suitable for Potassium-ion batteries (KIBs) anode material. Our results show that siligraphene not only own high stability of graphene but also own high capacity of silicene. And the theoretic capacity of g-SiC₅ and g-Si₂C₄ are 304.1 mA h/g and 128.6 mA h/g respectively for KIB. The average voltage is about 0.4 V, 0.3 V for g-SiC₅ and g-Si₂C₄. Meanwhile, based on the NEB calculations the low energy barrier of potassium ions diffused on the 2D-siligraphene, with the diffusion barrier is 132 meV for Si₂C₄ and 23 meV for SiC₅, show that this kind of anode materials might process a high migration rate; moreover, from the bandstructure calculations we might deduced that after absorbing potassium ion, siligraphene show excellent electrical conductivity. The molecular dynamics (MD) calculations were also show good stability of siligraphene absorbed potassium ion. Thus, siligraphene is promising anode material candidate for KIBs.