In Situ Transmission X-ray Microscopy Study on Working SnO Anode Particle of Li-Ion Batteries

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Abstract
The evolution of the interior microstructures of SnO during electrochemical lithiation/de-lithiation has been visualized by in situ transmission X-ray microscopy (TXM), complemented by in situ X-ray diffraction (XRD) to reveal phase information. A SnO secondary particle consisting of plates of primary particles has been shown to homogeneously expand during the first lithiation in two stages, including the first producing Li2O matrix that bears most original particle morphology and the second involving full lithiation of the precipitated Sn nano-particles from the first stage. Only the second stage is reversible upon de-lithiation, and the particle undergoes the reversible second-stage deformation during subsequent cycles. The results indicate clear advantages of using such a porous secondary SnO as the anode material in comparison with dense Sn particle previously revealed, including fast lithiation/de-lithiation kinetics, reduced overall volume expansion and enhanced mechanical robustness of the particle, supported by the Li2O backbones.