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The appearance of mechanical cracks originated from anisotropic expansion and shrinkage of electrode particles during Li de/intercalation is a major cause of the capacity fading in Li-ion batteries. Well-designed and controlled nanostructures of electrodes have shown a prominent prospect for solving this obstacle. Here, we report a novel and convenient strategy for the preparation of graphene nanoscroll wrapping NbO nanoparticles (denoted as T-NbO/G). First, high energy ball milling is conducted to acquire softly agglomerated T-NbO nanoparticles owing to its spontaneous reduction of surface energy among these single particles. Then freeze-drying leads to the formation of graphene nanoscroll, which easily realizes the in situ wrapping over softly agglomerated T-NbO nanoparticles. Extended cycling tests demonstrate that such T-NbO/G yields a high reversible specific capacity of 222 mA h g over 700 cycles at 1C. The dominated surface capacitive insertion processes possessing favorable kinetics enable T-NbO/G to exhibit excellent rate performance, which achieve a capacity of 110 mA h g at 10C. A combined ex situ X-ray diffraction, scanning electron microscopy, and transmission electron microscopy investigation reveal that the long-term cycling stability of T-NbO/G is attributed to the excellent structural stability of the electrode, in which the synergistic effect between the softly agglomerated T-NbO nanoparticles and graphene nanoscroll prevents the formation of mechanical cracks.

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Although significant advancements in the preparation of metal oxide hollow structures have been achieved, most synthesis routes have some complicated aspects such as requiring a hard-template, multistep procedures or other special reagents. This paper proposes a green and facile bubble-template approach to synthesize and organize Ni-Co hollow microspheres. The entire formation mechanism for the hollow spherical structures, including integration for nucleation, morphological tailoring and an Ostwald ripening process, has been elucidated based on time-dependent observations. The Ni-Co hollow microspheres revealed an excellent cycling stability (730 mA h g(-1) even after 140 cycles at 300 mA g(-1)) and good rate capability when evaluated as an anode material for lithium ion batteries (LIBs). The excellent electrochemical performance can be attributed to the rational design and organization of the hollow structures, which offer a large void space for accommodating volume changes, shorten the diffusion path for Li ions and electron transfer, as well as increase the contact area between the electrodes and electrolyte. Moreover, the synergistic effects of the nickel and cobalt ions with different lithiation potentials allowed the volume change to occur in a stepwise manner. The bubble-template strategy was convenient and very effective for constructing the hollow structures, and if well engineered, it could be extended to the synthesis of other advanced metal oxide anode materials for high energy storage devices and many other applications.