Vojtech Svoboda

Incremental Capacity Analysis and Close-to-Equilibrium OCV Measurements to Quantify Capacity Fade in Commercial Rechargeable Lithium Batteries

A quantitative approach is used to identify sources of contribution of capacity fade in commercial rechargeable lithium battery cells in laboratory evaluations. Our approach comprises measurements of close-to-equilibrium open-circuit voltage (cte-OCV) of the cell after relaxation at the end of the charging and discharging regimes and an incremental capacity analysis, in addition to conventional cycle-life test protocols using the dynamic stress test schedule. This approach allows us to separate attributes to capacity fade due to intrinsic and extrinsic origins.

In Situ Characterization of Electrochemical Polymerization of Methylene Green on Platinum Electrodes

A novel in situ characterization technique using imaging ellipsometry in conjunction with cyclic voltammetric (CV) deposition has been applied to correlate polymerized methylene green (poly-MG) film thickness and morphology, with charge transferred during CV cycles. We also report values for the refractive index (n) and extinction coefficient (k) of the monomer solution and the poly-MG film, for the first time. These values have been derived from measurements that employ multiple angles of incidence in the ellipsometry and analysis using an optical model based on Fresnel theory. The in situ characterization of film growth with thickness progression provided comprehensive information on the deposition process that could not be obtained using ex situ techniques such as scanning electron microscopy or optical microscopy. The results demonstrate the value of imaging ellipsometry as a quantitative characterization technique to monitor polymer film growth in situ and to characterize the quality of the film in terms of surface morphology and homogeneity as a function of film thickness. Comment is also provided on how the technique can be combined with other characterization techniques to deliver a more comprehensive analysis and control of the electrochemical deposition process.

In situ transient study of polymer film growth via simultaneous correlation of charge, mass, and ellipsometric measurements

Using three synchronized, in situ, nonintrusive, real-time characterization techniques to conduct transient observations, we revealed mechanistic details of a polymer film growth. A thin methylene green (MG) polymer coating (of the order of 35 nm) was used as a model system in this electrochemical microgravimetric imaging ellipsometry (EmIE) investigation. The direct correlation of changes in mass (via quartz crystal microbalance, QCM), ellipsometric angles (via imaging ellipsometry) with electrochemical conditions (in cyclic voltammetry, CV) provides discrete temporal and spatial information to help us decipher the underlying steps, from which we were able to separate adsorption, reduction, oxidation, desorption, and polymerization regimes involved in the deposition process. The evidence revealed in this study could have broad impact on the general understanding regarding how a film is deposited onto a metal surface.