Inhibiting Sn coarsening to enhance the reversibility of conversion reaction in lithiated SnO2 anodes by application of super-elastic NiTi films

Abstract

The large capacity loss and low initial Coulombic efficiency (ICE) of a conventional SnO2-based anode for Li ion batteries are originated largely from the limited reversibility of the conversion reaction associated with the anode. Often, the reversibility of the lithiation/delithiation of SnO2 (with a high ICE value of ∼82%) declines with Sn coarsening in the Sn/Li2O mixture during cycling, leading to gradual capacity decay. Here we demonstrate that the application of super-elastic films of NiTi alloy could accommodate the internal stress and volume change of lithiated nano-SnO2 layer in a tri-layer NiTi/SnO2/NiTi sandwich anode, effectively suppressing Sn coarsening. This unique electrode configuration has helped to retain the high reversibility of the SnO2 layer with reversible capacity more than 800 mAh/g (based on SnO2) for over 300 cycles, demonstrating stable charge capacities of ∼400 mAh/g in the potential ranges of 0.01–1.0 V and 1.0–2.0 V(vs. Li/Li+), respectively. Insitu spectroscopic and exsitu diffraction analyses corroborate the highly reversible electrochemical cycling, confirming that the reversibility and cyclability of SnO2 anodes can be dramatically enhanced by preserving the nanostructure of Sn/Li2O mixture, which facilitates the reversible conversion reaction.