Designed Synthesis of SnO2 Nanosheet Arrays with Superior Performance for Lithium and Sodium Storage

Room-temperature rechargeable sodium-ion batteries (SIBs) are receiving increasing attention for upcoming large-scale applications in smart grid and electric vehicles due to the earth abundance and low cost of sodium.^{1, 2} However, Na ion has a larger radius of 1.02 Å (~55% larger than Li⁺, 0.76 Å) and three times heavier than lithium (23 g mol^-1 compared with 6.9 g mol^-1), which directly affects the Na⁺ insertion/deinsertion in electrochemical process, leading to low reversible capacity, poor cycling stability, inferior rate capability.³ Although reversible sodium intercalation into commercial graphite anodes was demonstrated by using diglyme-based electrolyte or chemically modified graphite recently, the specific capacity is still lower than that of lithium ion batteries.^{4, 5}Therefore, it is highly promising to develop high capacity anode materials based new storage mechanisms toward practical application of SIBs.

Fig. 1 (a) XRD pattern, (b-d) SEM images of SnO₂ nanosheet arrays grown on the carbon fiber paper.

Herein, we report a simple solution-based hydrothermal approach to construct hybrid architectures by growing 2D hierarchical SnO₂ nanosheet arrays on conductive flexible carbon substrates as the anode for Na-ion and Li-ion batteries. Fig. 1a shows the X-ray diffraction (XRD) pattern of the SnO₂ nanosheet arrays, and all the diffraction peaks can be readily indexed to the tetragonal phase of SnO₂ (JCPDS Card no.71-0652). Two peaks at around 26.2° and 43.1° marked with asterisk originate from the carbon textiles.⁶ Scanning electron microscopy (SEM) images shown in Fig1b-d clearly display ultrathin SnO₂ nanosheet arrays uniformly cover carbon substrates and interconnect with each other to form highly open and porous structure. Taking merits of the ultrathin and highly conductive nature of SnO₂ nanosheets as well as the porous interconnected three-dimensional nanoarchitectures, the binder-free flexible SnO₂electrodes exhibit high specific capacity with enhanced cycling stability, making it a promising anode material for electrochemical energy storage devices application.

 Acknowledgements

The authors are grateful for financial support from the National Program on Key Basic Research Project of China (973 Program, no. 2014CB239701), National Natural Science Foundation of China (no. 21173120, 51372116), Natural Science Foundations of Jiangsu Province (no.BK2011030), Funding for Outstanding Doctoral Dissertation in NUAA (no.BCXJ14-12), Founding of Graduate Innovation Center in NUAA (no. kfjj201438), and Funding of Jiangsu Innovation Program for Graduate Education (no.KYLX_0254) and the Fundamental Research Funds for the Central Universities.

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