Tin dioxide (SnO₂) has been considered one of the most promising alternative anode materials for lithium batteries. In the past two decades, extensive studies have been directed to gaining a fundamental understanding of the lithiation/delithiation reactions to improve the performance of SnO₂-based electrodes. However, the realization of full capacity of SnO₂ anode has been hindered by the large initial irreversible capacity loss characterized by low initial Coulombic efficiency (ICE). This is generally attributed to the inferior reversibility of conversion reactions between Sn⁰/Li₂O mixture and SnO₂, and highly correlated to the poor stability of the nanostructure of Sn/Li₂O mixture.

Here we demonstrated that Li₂O can indeed be highly reversible in a SnO₂ electrode with controlled nanostructure and achieved an initial Coulombic efficiency of ~95.5%, much higher than that previously believed possible (52.4%). Insitu spectroscopic and diffraction analyses corroborate the highly reversible electrochemical cycling, suggesting that the interfaces and grain boundaries of nano-sized SnO₂ may suppress the coarsening of Sn and enable the conversion between Li₂O and Sn to amorphous SnO₂ when de-lithiated [1]. Furthermore, we have found that the application of super-elastic films of NiTi alloy could accommodate the internal stress and volume change of lithiated nano-SnO₂ layer and thus effectively suppress Sn coarsening, to retain the high reversibility of the SnO₂ layer with reversible capacity more than 800mAh/g (based on SnO₂) for over 300 cycles, demonstrating stable charge capacities of ~400mAh/g in the potential ranges of 0.01-1.0V and 1.0-2.0V(vs. Li/Li⁺), respectively[2].

To greatly enhance the stability of the Sn nanostructure and the reversibility of conversion reactions in lithiated SnO₂, a series SnO₂-M-G (M=Fe, Mn, Co) ternary nanocomposites have been produced by scalable ball milling [3]. The SnO₂-M-G nanocomposites demonstrate very high ICEs of up to 88.6%, which is the highest values among those reported so far for SnO₂-based powder anodes. The SnO₂-Fe-G maintains a capacity of 1338 mAh/g after 400 cycles at a current rate of 0.2 A/g, while the SnO₂-Mn-G retains an excellent long-term stable capacity of 700 mAh/g throughout 1300 cycles at 2 A/g. Even in soft-packing full cells constructed with LiMn₂O₄ cathode, a high capacity retention of 85.1% can be maintained after 100 cycles operating in the range 0.5–3.8 V. All these data indicate the promising potential of SnO₂-M-G as an interface material for high-performance anodes in lithium ion batteries.

References:

[1] R. Hu, D. Chen, G. Waller, Y. Ouyang, M. Zhu, M. Liu. Dramatically enhanced reversibility of Li₂O in SnO₂-based electrodes: the effect of nanostructure on reversible capacity Energy Environ. Sci., 2016, 9: 595.

[2] R. Hu, Y. Ouyang, D. Chen, H. Wang, M. Zhu, M. Liu. Inhibiting Sn coarsening and enhance the reversibility of conversion reaction in lithiated SnO₂ anodes by application of super-elastic NiTi films Acta Mater., 2016, 109:248

[3] R. Hu, Y. Ouyang, T. Liang, H. Wang, J. Chen, M. Zhu. Stabilizing nanostrucutre of SnO₂ anodes by transition metals: a route to achieve high initial Coulombic efficiency and stable capacities for lithium storage Adv. Mater., 2016, in press