2D-Nb<sub>2</sub>CT<sub><i>z</i></sub>-Supported, 3D-Carbon-Encapsulated, Oxygen-Deficient Nb<sub>2</sub>O<sub>5</sub> for an Advanced Li-Ion Battery
Junfeng Huang, Teng Sun, Meiyi Ma, Zhong Xu, Yuchen Wang, Yanting Xie, Xiang Chu, Xinglin Jiang, Yongbin Wang, Shenglong Wang, Weiqing Yang, Haitao Zhang
Abstract
Exploring advanced electrode materials with rapid lithium-ion charging/discharging kinetic properties is significant for the development of modern electric transportation. Herein we report a powerful synergistic engineering of carbon encapsulation and oxygen deficiency to construct Nb2O5 through a two-step method of pregelation and annealing treatment. The yielded Nb2O5 with sufficient oxygen vacancies are supported by 2D highly conductive Nb2CTz (T = O, OH, and F) MXene and further encapsulated by 3D carbon layers (2D/3D Nb2O5–x). Such an exquisite architecture is proved to efficiently overcome the intrinsic weakness of slow ion transfer, low electrical conductivity, and long-term cycling instability in metal oxides, in this case Nb2O5. Consequently, 2D/3D Nb2O5–x composites share an improved average diffusion coefficient from 1.34 × 10–12 cm–2 s–1 to 3.02 × 10–12 cm–2 s–1, a facilitated Li+ ion diffusion pathway, and shortened relaxation time constant (τ0) from 8.9 to 6.1 ms. In an optimized 2D/3D Nb2O5–x electrode, it delivers a high capacity of 245 mAh g–1 at 0.1 C (1 C = 270 mA g–1), 85 mAh g–1 at a high rate of 5 C, and an excellent long-term durability with 92.7% capacity retention during 1250 cycles. These results clearly demonstrate the significance of tailoring the microstructure and composition of metal oxides as used in high-rate and long-cycling lithium-ion storage.