The development of high–capacity anode materials for lithium ion batteries (LIBs) is a key step toward achieving large–scale energy storage applications for portable electronic devices, electrical vehicles, and hybrid electrical vehicles.¹ Since its first discovery, the current commercial LIBs have been using graphite as anode material. Although this carbon–based anode is cheap, abundant and reliable, however it provides a limited theoretical capacity of 372 mAh/g, hence hampering the establishment of high–energy density LIBs to meet huge technological demands in the near future.² To replace the incumbent anode, intensive research has been devoted on the alloy–based materials such as silicon, germanium, tin, and tin oxide (SnO₂). Among these candidates, SnO₂ is a promising anode material attributing to its low cost, nontoxicity, low operating potential (0.25 V vs. Li/Li⁺), high theoretical capacity (782 and 1,493 mAh/g for alloying/de–alloying and both alloying/de–alloying and conversion reaction, respectively), and easy synthesis in regard to nanostructures.³ It was widely studied that employing the pristine SnO₂ anode for LIBs may face a significant barrier because of a severe volume change during the electrochemical cycle, causing pulverization and cracks and eventually the loss of electrical conduction paths. In the meantime, the new–fresh cracks that are exposed to the electrolyte may form a continuous solid electrolyte interphase (SEI)–filming process resulting in a thickened SEI layer on the surface of SnO₂ anode. Consequently, the cell cannot avoid a rapid capacity fading.⁴

To overcome these problems, we synthesized the rational anode material consisting of hierarchical structure and dual carbon layers. The hierarchical structures of SnO₂ anode are aimed at increasing the active surface area, allowing more Li ions can be stored in the spaces, thus promoting a faster Li ion diffusivity. In addition, dual carbon layers are aimed at alleviating the volume change during charge-discharge reaction, leading to mechanically keep the structure of electrode stable and enhance the ionic conductivity at the interfaces. As the results, our C@SnO₂@C anode demonstrated a significant electrochemical performance such as long cycle life and high reversible capacity, hence postulating a solution for commercialization of Sn-based anode for LIBs in the market.

[References]

1. Chen, Y. M.; Lu, Z. G.; Zhou, L. M.; Mai, Y. W.; Huang, H. T. Triple–coaxial electrospun amorphous carbon nanotubes with hollow graphitic carbon nanospheres for high– performance Li ion batteries. Energy Environ. Sci. 2012, 5, 7898–7902.

2. Ko, Y. N.; Park, S. B.; Kang, Y. C. Design and fabrication of new nanostructured SnO₂–carbon composite microspheres for fast and stable lithium storage performance. Small 2014, 10, 3240–3245.

3. Thomas, R.; Rao, G. M. SnO₂ nanowire anchored graphene nanosheet matrix for the superior performance of Li–ion thin film battery anode. J Mater Chem A 2015, 3, 274–280.

4. Zhu, C. R.; Xia, X. H.; Liu, J. L.; Fan, Z. X.; Chao, D. L.; Zhang, H. et al. TiO₂ nanotube@SnO₂ nanoflake core–branch arrays for lithium–ion battery anode. Nano Energy 2014, 4, 105–112.