Advanced Electrode Design with Homogenous Electric Field Distribution to Study the Electrochemical Li Deposition on Carbon Electrodes by Means of In Situ TEM

A detailed understanding of the early stage Li dendrite formation as well as of the solid electrolyte interphase (SEI) formation at the electrode/electrolyte interface is indispensable in mitigating the degradation in battery performance and the safety issues for Li batteries, as well as in developing other energy materials. <i>In</i><i> situ</i> electrochemical transmission electron microscopy (ec-TEM) is a powerful tool to investigate the Li deposition process in its very early stage during the electrochemical cycling of Li battery materials. It has been demonstrated so far that real-time observation of electrochemically induced Li nucleation, growth, and dendrite formation can be achieved with high spatial resolution on the glassy carbon as well as on metal (platinum or gold) electrodes <i>in situ</i> by using meanwhile commercially available microscale ec-TEM liquid cells. However, the so far reported ec-TEM cells feature inhomogeneous electric field distribution along the electrodes, which may cause unreliability of the measurement and set tight limits for the interpretation and the quantitative analysis. Thus, this persuasive characterization technique is still kept far from a “close to real” application scenario.<br/>Here, we report an advanced electrode design enabling a homogenous electric field distribution for further microscopic quantitative characterization of the early-stage Li deposition in a closer approximation to the actual battery scenario. Similar to the commercially available chips, the designed ec-TEM chips are equipped with a semicircle carbon electrode as the working electrode surrounding two platinum wires in the same shape as reference and counter electrodes. The design is based on COMSOL 3D simulations, which demonstrate the electric field distribution and allow for a quantitative comparison of the designed chips with the commercially available ones. Experimental investigations on metal deposition from liquid electrolytes (Li and other reference materials) using the designed ec-TEM chips were performed and these analyses demonstrated the advancement and feasibility of the newly designed electrode configuration to approach true battery conditions. These designed ec-TEM chips facilitate the quantitative electrochemical characterization combined with the <i>in situ</i> TEM technique not only relevant for Li battery research but for any kind of electrochemical processes, where the deposition of active compounds from liquid electrolytes represents an elementary mechanistic step in the overall process.