Electrochemistry of Lithium-ion transport kinetics in ionic liquids

Lithium-ion technology is ubiquitous in the contemporary society in varied applications. This is primarily because of their high volumetric and gravimetric energy density, which is unmatched by any other alkali metal ion. State-of-the art cells today reach nearly 700 Wh/L and further ambition for next generation batteries target 1000 Wh/L, which can be realised through Li metal anodes in conjunction with solid state electrolytes. At the heart of this futuristic technology is the process of continuous plating and stripping of Lithium during cycling of the battery. Owing to the highly reactive nature of Li, this is a complicated process shadowed with several complications during both plating (for e.g., dendrite formation and growth, dead lithium, continuous interface change, short circuit etc.) and stripping (void formation, pitting, broken interface layers etc.). Electrode architecture and the choice of electrolytes are some of the key factors that affect electrochemical performance of Li anode. 

Here at imec, we are evaluating various ionic liquid-based electrolytes (ILEs) for successfully mitigating the issues faced by Li anodes. Of interest here is to investigate the mass transport properties of Li+ ions in ILE’s with/without additives. In ILE’s, the Li+ solvation affects ionic radii, free solvent concentration, electrochemical activity, mass transport etc. which can be drastically altered by adding certain solvent additives to modify Li plating/stripping characteristics. In this project, the transport properties of Li+ ions during plating/stripping will be studied on rotating disk electrode (RDE) to study these effects. By varying the concentration of Li salt/rotation speed, diffusion coefficients in ILE’s with various additives can be estimated. In addition, other parameters like exchange current density and transfer coefficients will also be compared for different ILE/additive combinations. Such fundamental knowledge can be a starting point to successfully engineer superior functioning Li anode/electrolyte combinations. 

The prospective student will screen and prepare several ILE/solvent additive combinations, measure their kinematic viscosities, and perform electrochemical measurements on a RDE inside a glove box. The determined diffusion coefficient values for known systems will be compared with literature as a proof measurement, followed by measurements in actual test combinations. The successful combinations of ILE/additives will then be utilized in test Li symmetric cells.