Hierarchically structured C@SnO₂@C nanofiber bundles with high stability and effective ambipolar diffusion kinetics for high-performance Li-ion batteries

The implementation of transition metal oxides as anode materials for Li-ion batteries (LIBs) has been largely hindered by their huge volumetric change during the lithiation/delithiation cycles, which generally leads to electrode pulverization with a fast capacity fading. Slow ambipolar (ionic and electronic) diffusion kinetics are another disadvantage suffered by transition metal oxides. This intrinsic drawback inevitably causes a poor rate capability of transition metal oxides. SnO₂ is an attractive candidate as an anode material for next-generation LIBs due to its high theoretical capacity, low cost and improved safety. In this article, a sandwich-structured carbon nanofiber@SnO₂@carbon coating (C@SnO₂@C) nanofiber bundle was facilely prepared by using collagen fiber, a typical fibrous protein, as the biotemplate as well as the carbon source. The hierarchical architecture of the C@SnO₂@C nanofiber bundle guaranteed a good match between the electron transport kinetics and the Li⁺ diffusion kinetics, thus realizing efficient ambipolar diffusion. Another merit that originated from the configuration of the C@SnO₂@C nanofiber bundle was the unique “breath” behavior, which effectively accommodated the volume change of SnO₂ so as to ensure structural integrity with the formation of the smooth and thin solid electrolyte interphase (SEI). The C@SnO₂@C nanofiber bundle showed obvious advantages both in rate capability and cycling stability as compared with those of conventional carbon/SnO₂ nanocomposites, including a C@SnO₂ nanofiber bundle and SnO₂@C nanofiber bundle. Our strategy developed here may be extended for the synthesis of other high-performance anode materials, especially for transition metal oxides that suffered from poor electrical conductivity and/or huge volumetric change.