Interpenetrating graphene network bct-C₄₀: a promising anode material for Li ion batteries

The stable sp²-C atoms in graphite enable its excellent structural and electrochemical stability as an anode material for Li-ion battery applications, while the limited Li-storage capacity of graphite also originates from the sp² hybridization. Herein, from first-principles calculations, we show that a synergistic effect of sp² and sp³ hybridized C atoms can substantially enhance the Li-storage performance in carbon-based anodes, using bct-C₄₀ as an example, which is constructed with interconnected graphene layers (sp² hybridized C atoms) and the connecting points are composed of sp³-C atoms. Charge transfer from sp²-C atoms to sp³-C atoms has been found, leading to unoccupied electronic states forming around the Fermi level. Furthermore, we found that the unoccupied electronic states are contributed by the p_z orbital of the sp²-C atoms, resulting in stronger interactions between C atoms and intercalated Li atoms. As a result, the Li intercalation concentration in bct-C₄₀ can reach as high as LiC_2.5 (corresponding to a capacity of 893 mA h g^-1), much higher than that of LiC₆ in graphite (372 mA h g^-1). Furthermore, bct-C₄₀ inherits good structural and electrochemical stability, a metallic electronic structure, and low Li-ion migration energy barriers (0.067-0.112 eV) from the sp² hybridized graphene structures, therefore very good Li-storage performance is expected, indicating that bct-C₄₀ can be used as a high-performance anode material for lithium ion batteries. Our study provides new insights into the functionality of sp²- and sp³-C atoms in carbon-based anode materials and is helpful for the designing of new carbon-based anodes.