Q-Carbon: A New Carbon Allotrope with a Low Degree of s-p Orbital Hybridization and Its Nucleation Lithiation Process in Lithium-Ion Batteries.

A novel metallic carbon allotrope, Q-carbon, was discovered using first-principles calculations. The named Q-carbon possessed a three-dimensional (3D) cage structure formed by carbon atoms with three ligands. The energy distribution of electrons in different orbitals revealed that Q-carbon has a low degree of s-p orbital hybridization. The calculated Li binding energies suggested Li aggregation inside Q-carbon during lithiation. As a result, a LiC phase was formed and gradually expanded in Q-carbon, implying a typical two-phase transition. This allowed Q-carbon to have a constant theoretical voltage of 0.40 V, which effectively inhibited Li dendrite formation. A stable LiC/C two-phase interface was confirmed by stress-strain analysis, and a calculated Li diffusion barrier of ∼0.50 eV ensured effective Li diffusion along a 3D pathway. This study was of great significance for the understanding of two-phase transition of Li storage materials and provided a new insight into the design of new carbon materials for energy storage applications.