In-Situ Growing Mesoporous CuO/O-Doped g-C₃N₄ Nanospheres for Highly Enhanced Lithium Storage

The development of lithium-ion batteries using transition metal oxides has recently become more attractive, due to their higher specific capacities, better rate capability, and high energy densities. Herein, the in situ growth of advanced mesoporous CuO/O-doped g-C₃N₄ nanospheres is carried out in a two step hydrothermal process at 180 °C and annealing in air at 300 °C. When used as an anode material, the CuO/O-doped g-C₃N₄ nanospheres achieve a high reversible discharge specific capacity of 738 mAhg^-1 and a capacity retention of ∼75.3% after 100 cycles at a current density 100 mAg^-1 compared with the pure CuO (412 mAhg^-1, 47%) and O-doped g-C₃N₄ (66 mAhg^-1, 53%). Even at high current density 1 Ag^-1, they exhibit a reversible discharge specific capacity of 503 mAhg^-1 and capacity retention ∼80% over 500 cycles. The excellent electrochemical performance of the CuO/O-doped g-C₃N₄ nanocomposite is attributed to the following factors: (I) the in situ growing CuO/O-doped g-C₃N₄ avoids CuO nanoparticle aggregation, leading to the improved lithium ion transfer and electrolyte penetration inside the CuO/O-doped g-C₃N₄ anode, thus promoting the utilization of CuO; (II) the porous structure provides efficient space for Li⁺ transfer during the insertion/extraction process to avoid large volume changes; (III) the O-doping g-C₃N₄ decreases its band gap, ensuring the increased electrical conductivity of CuO/O-doped g-C₃N₄; and (IV) the strong interaction between CuO and O-doped g-C₃N₄ ensures the stability of the structure during cycling.