A robust strategy for stabilizing SnO2: TiO2-supported and carbon-immobilized TiO2/SnO2/C composite towards improved lithium storage
Introduction
Thanks to the high theoretical capacity of ca. 782 mAhh g−1, SnO2 has attained wide attention as a promising alternative anode material to low capacity graphite in recent decade [1], [2], [3]. However, there are still two crucial issues SnO2 anode has been suffering from need to be urgently solved to promote the development of SnO2-based anodes in lithium-ion battery application [4], [5], [6], [7], [8]. One is the inferior conductivity, which severely constraints on rate property of SnO2, namely the power density of batteries which is the one of pressing need performances for new generation high performance lithium-ion batteries (LIBs). The other one is the painful huge volume change during charge/discharge process, which results in the capacities of SnO2 anode fade quickly and, at the same time not only affected the capacity but also the life of SnO2 anodes [9], [10], [11]. Therefore, huge efforts have been made to explore and develop desirable strategies to solve above problems.
After years of research, it is acknowledged that elaborately compositing the nanostructure of SnO2 with good conductive and flexible carbonaceous materials is an effective strategy for solving the problems mentioned above and hence widely applied in SnO2 anode research field [12], [13], [14], [15]. The nanostructure of SnO2 can not only alleviate the absolute volume change but also the diffusion distance of lithium-ions and electrons. More importantly, the good conductive and flexible carbonaceous materials can not only upgrade the conductivity of composite electrodes but also effectively cushion the volume change of SnO2. Thus, the composites consist of SnO2 and carbonaceous materials (SnO2/C) can blend the merits of both SnO2 and carbonaceous materials to achieve a perfect synergistic effect to improve the performances of SnO2-based anodes such as capacity, rate and life properties. As might have been expected, the reported state-of-the-art SnO2/C anodes, such as carbon-coated SnO2 submicroboxes, SnO2-carbon hybrid hollow spheres and so on, exhibited greatly improved performance when compared to the nanostructure of pure SnO2 counterparts [16], [17]. In addition, in order to further ameliorate the structure stability of SnO2/C, namely cycling performance, the TiO2 materials known as excellent structure stability are extensively used as structure supports to combine with SnO2/C composites (TiO2/SnO2/C) [18], [19], [20], [21], [22], [23], [24], [25], [26], [27], [28]. In consequence, the TiO2/SnO2/C composites showed longer life than that of SnO2/C counterparts, but the capacities of TiO2/SnO2/C composites were weakened to a certain extent due to the low practical theoretical capacity of TiO2 materials (about 168 mAhh g−1). Undoubtedly, it is crucial to design and fabricate an effective hetero-structure to ensure that the TiO2/SnO2/C could exhibit satisfying electrochemical performance in terms of specific capacity, rate capability and life via taking full advantage of the synergistic effect of these components.
Herein, TiO2 nanobelts were used as structure-support to composite with SnO2/C to construct an unique hetero-nanostructure of TiO2 SS@SnO2@C composite, and the whole preparation process of TiO2 SS@SnO2@C only experiences facile two steps, one is the hydrothermal treatment, the other is the carbonization, as shown in Fig. 1. It can be clearly seen that the nano-cluster assembled by SnO2 nanoparticles are dispersed on the TiO2 nanobelts and further immobilized by conformal carbon coating. Thanks to the perfect synergistic effect of SnO2 nano-cluster, TiO2 nanobelts and conformal carbon coating, the impressive electrochemical performance of as-prepared TiO2 SS@SnO2@C anode is achieved. In addition, it is suggested that the simplified preparation process would play an important role in the development of anode materials.
Section snippets
Preparation of TiO2 SS@SnO2@C composite
All chemicals (analytical grade) were purchased from Shanghai Aladdin biochemical technology co., LTD and used without further purification. In a typical process, 1 ml of tetrabutyl titanate was slowly dropped into 20 ml of 10 M NaOH aqueous solution and subsequently stirred for 30 min. The obtained white suspension was carefully transferred into a Teflon-lined stainless steel autoclave and placed in an oven heated to 180 °C in advance for 24 h. When the autoclave naturally cooled down to room
Result and discussion
The TEM and SEM techniques are applied to systematically research the microstructures of resultant TiO2 SS@SnO2@C. Fig. 1a-c give the TEM images of TiO2 SS@SnO2@C with different magnifications. We can obviously find that the TiO2 SS@SnO2@C well reserves the one-dimensional nanobelt morphologies of HTO nanobelts after hydrothermal and carbonization treatment when compared to the SEM images of HTO nanobelts (Figs. S1(a and b)). But, it is interesting that the surface of TiO2 SS@SnO2@C becomes
Conclusions
In summary, a hybrid TiO2 SS@SnO2@C consist of one-dimensional TiO2 nanobelts, zero-dimensional SnO2 nanoparticles and conformal carbon coating has been fabricated by a facile approach. It is demonstrated that the perfect synergistic effect of these components with different dimensional nanostructures provides improved electrochemical kinetic and outstanding structure stability for the TiO2 SS@SnO2@C electrodes. As a result, the TiO2 SS@SnO2@C electrodes exhibit outstanding lithium storage
Acknowledgments
We are grateful for financial support from Scientific Research Start-up Foundation of Zhejiang Sci-Tech University (Grant no. 11432932611706).
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