2D-Nb2CTz-Supported, 3D-Carbon-Encapsulated, Oxygen-Deficient Nb2O5 for an Advanced Li-Ion Battery

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 Nb 2 O 5 through a two-step method of pregelation and annealing treatment. The yielded Nb 2 O 5 with sufficient oxygen vacancies are supported by 2D highly conductive Nb 2 CT z (T = O, OH, and F) MXene and further encapsulated by 3D carbon layers (2D/3D Nb 2 O 5– 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 Nb 2 O 5 . Consequently, 2D/3D Nb 2 O 5– 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 (τ 0 ) from 8.9 to 6.1 ms. In an optimized 2D/3D Nb 2 O 5– 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.