In situ TEM Studies of Nanocrystal Composition, Structure, and Phase

In-situ transmission electron microscopy (TEM) allows researchers to analyse at the nano-scale and in ‘real time’ the electrochemical processes of the electrode materials within batteries during device operation. The active interface regions of such electrodes form solid electrolyte interface (SEI) layers during the charge and discharge cycling. The formation and movement of this functional SEI nano-interface is one of the main research fields in battery science, as it directly affects battery performance and lifetime. Of particular interest is observing the structural and chemical evolution of this lithium-rich, extremely complex polycrystalline interface.

Si nanowires are attractive materials for applications such as lithium battery anodes due to their high theoretical capacity and ultra-low-cost for material sourcing and fabrication. The use of electrochemically active metals such as Sn for the growth of Si nanowires contributes to the overall specific capacity of the electrode. This study explores the phase change in both the Si nanowire metal seed head and the nanowire SEI layer during battery cycling. Our goal is to investigate the effect a chosen seed metal has on the Si electrode. We show that the lithiation/delithiation behaviour of the Sn-Si nanowire obtained using liquid cell was comparable to the result from bulk half-cell cycles and ex-situ analysis. Finally, we compare the benefits and drawbacks of liquid cell in-situ electrochemistry to cryogenic TEM analysis of the same system. Although in-situ electrochemistry TEM offers many advantages over other characterisation techniques, this analysis method is still in its infancy.

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