Highly microporous graphite-like BCxO3−x/C nanospheres for anode materials of lithium-ion batteries

Abstract

In the present work, we report Li storage in a spherical graphite-like BC_xO_3−x/C (g-BCO/C) nanostructure with an average diameter of ca. 75 nm. Highly microporous g-BCO/C nanospheres with a BET specific surface area of 493.35 m² g⁻¹ were fabricated via a simple hydrothermal carbonization process combined with one-step annealing. The microstructure of the g-BCO/C nanospheres was characterized by means of XRD, TEM and Raman spectroscopy. XPS measurements reveal the formation of a boron solid-solution phase such as BC₃ (x = 3), BC₂O (x = 2) and BCO₂ (x = 1), as well as the concentration of substitutional boron which is around 1.75 at.%. Further, ¹¹B-NMR spectra confirmed the formation of BC₃. Benefiting from the unique structural features and boron doping, the g-BCO/C nanospheres exhibit excellent electrochemical performances as an anode material for Li-ion batteries. A high initial reversible capacity (591 mA h g⁻¹, 200 mA g⁻¹) and high-rate capacity (262 mA h g⁻¹, 1000 mA g⁻¹), as well as stable capacity (446 mA h g⁻¹, 200 mA g⁻¹) after 100 cycles are delivered. The improved Li storage performance is attributed to three merits of g-BCO/C nanospheres: the large number of edge defects induced by boron, the micropores in the material and the large spacing of the lattice fringes (d₀₀₂) which can provide extra Li storage regions.