Given the inherent features of open tunnel-like structures,
moderate
lithiation potential (1.0–3.0 V vs Li/Li+), and
reversible redox couples (Nb5+/Nb4+ and Nb4+/Nb3+ redox couples), niobium-based oxides with
Wadsley–Roth crystallographic shear structure are promising
anode materials. However, their practical rate capability and cycling
stability are still hindered by low intrinsic electronic conductivity
and structural stability. Herein, ultrathin carbon-confined Nb12O29 materials with rich oxygen vacancies (Nb12O29–x
@C) were designed
and synthesized to address above-mentioned challenges. Computational
simulations combined with experiments reveal that the oxygen vacancies
can regulate the electronic structure to increase intrinsic electronic
conductivity and reduce the Li+ diffusion barrier. Meanwhile,
the carbon coating can enhance structural stability and further improve
the electronic conductivity of the Nb12O29 material.
As a result, the as-prepared Nb12O29–x
@C exhibits high reversible capacity (226 mAh g–1 at 0.1 A g–1), excellent high-rate
performance (83 mAh g–1 at 5.0 A g–1), and durable cycling life (98.1% capacity retention at 1.0 A g–1 after 3000 cycles). The lithium storage mechanism
and structural stability of Nb12O29–x
@C were also revealed by in situ X-ray diffraction (XRD), ex situ X-ray photoelectron
spectroscopy (XPS), and ex situ Raman spectroscopy.
When applied as the anode of lithium-ion capacitors (LICs), the as-built
LIC achieves high energy density (72.4 Wh kg–1)
within the voltage window of 0.01–3.5 V, demonstrating the
practical application potential of the Nb12O29–x
@C materials.