Coupling Phenomena Between Micromorphological Evolution and Ionic Mass Transfer Rate during Ag Electrodeposition in AgNO3 Aqueous Solution

The rechargeable battery concept with maltreat tolerance and safety is essentially indispensable not only in the space application but also in terrestrial renewable energy storage systems. Higher energy density, power capability and longer life requirements make the targets more challenging.  A better understanding of the electrolyte/electrode interface phenomena including electrode kinetics is crucial.  “Electrochemical Nucleation & Growth” aspect is a fundamental approach how to control the coupling phenomena between nano-structural interface evolution and ionic mass transfer rate enclosed a meso-scale space filled with electrolyte.    Such a research has not been frequently challenged in designing the longer life energy storage devices. 

Metal negative electrode surface shows various morphologies after repetition of electrodeposition and electrochemical dissolution reaction.  Dendrite precursor is finally grown after electrochemical nucleation and growth process where the coupling phenomena govern.  It is also indispensable for us to prolong the charging/discharging operation of secondary battery after longer term utilization under various environments.  For liquid electrolyte, a precise study of these morphologies may be complicated by convective motion caused by gravitational force of buoyancy.  Now the coupling phenomena are discussed in the case of silver because it has been employed as negative electrode in space application.  

3M AgNO₃ aqueous solution was contained in a quasi-2D cell. Holographic interferometry was employed to monitor the ionic mass transfer rate. The concentration profiles were formed around dendrite tips of silver electrodeposited at extremely high current densities.     A uniform diffusion layer was formed along the cathode surface at the start of electrolysis.  Following a certain incubation period, several dendrite tips began to protrude into the diffusion layer.  The growth rates of these dendrites were related to concentration gradients around the tips, diffusivity, and transfer number of Ag⁺ ion.  Giant-Macro step flow accompanied with Ag dendritic growth was dynamically observed with Laser Confocal Scanning Microscope.  

Transient current variation measurements are now engaged under the double pulse potential which introduces Ag nucleus on the foreign substrate in order to develop a multi-scale physical model of dendritic growth.