Toward Reversible Conversion Reactions and High Initial Coulombic Efficiency in Lithiated SnO2 Based Anode Materials
Authors: Hu Renzong 
Published: February 2020

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%). I
nsitu 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