We developed electrochemical liquid cells for transmission electron microscopy (TEM), which allows imaging electrochemical processes in liquid electrolyte with high spatial resolution in real time. Using this set up, we have studied the electrochemical deposition and dissolution of lead dendrites on gold electrodes immersed in an aqueous solution of lead nitrate. Observation reveals lead dendrites are developed by the fast protrusion of lead branches in the electrolyte and tip splitting. A unique electrochemical growth of single crystal dendrites through nucleation, aggregation, alignment and attachment of randomly oriented small grains has been identified. Using the same development, we have also directly visualized electrochemical lithiation and delithiation of Au anodes in commercial LiPF6/EC/DEC electrolyte for lithium ion batteries. A cyclic voltammetry with voltage range of 0 ~ -3 V and a scan rate of 0.1 V/s was first applied on the electrodes. At the early stage bubbles formed by decomposition of electrolyte was observed, subsequently lithiation of gold electrode followed by the growth and dissolution of lithium dendrites was captured. We have also observed the growth and evolution of solid electrolyte interface (SEI) thin film on the other electrode at the applied cyclic voltammetry in the range of 4 ~ 0 V. There was an initial fast growth of SEI and the growth rate dropped to almost zero when the voltage was decreased to 0 V. And, the initial thin film on the Au electrode was compact with no gap between the thin layer and the Au electrode. Then a gap between the SEI film and the electrode started to grow and the gap almost stopped when the applied voltage was decreased to zero. In situ study of electrode-electrolyte interfaces shed lights on strategies of improving electrode design for better performance and reducing short-circuit failure in lithium ion batteries.

Visualization of interfaces between electrode and liquid electrolyte by in-situ TEM: Applications in energy storage

247th National Meeting (2014)

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