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Separators play an important role in lithium-ion battery operation; however, no comprehensive studies of their microstructure and its impact exist. To enable such studies, we present a simple method for separator microstructure visualization and quantification based on focused-ion-beam scanning electron microscopic tomography. Here, we use this approach to visualize a sample of commercial polyethylene separator, calculate its directional effective transport parameters, and explain the impact of these values on battery performance. We further extend this technique to visualize metallic deposition within the separator, which could facilitate the study of lithium plating and dendritic growth., Journal of the Electrochemical Society, 163 (6), ISSN:0013-4651, ISSN:1945-7111

The permeability barrier of nuclear pore complexes (NPCs) controls bulk nucleocytoplasmic exchange. It consists of nucleoporin domains rich in phenylalanine-glycine motifs (FG domains). As a bottom-up nanoscale model for the permeability barrier, we have used planar films produced with three different end-grafted FG domains, and quantitatively analyzed the binding of two different nuclear transport receptors (NTRs), NTF2 and Importin b, together with the concomitant film thickness changes. NTR binding caused only moderate changes in film thickness; the binding isotherms showed negative cooperativity and could all be mapped onto a single master curve. This universal NTR binding behavior – a key element for the transport selectivity of the NPC – was quantitatively reproduced by a physical model that treats FG domains as regular, flexible polymers, and NTRs as spherical colloids with a homogeneous surface, ignoring the detailed arrangement of interaction sites along FG domains and on the NTR surface., eLife, 5, ISSN:2050-084X

We discuss physicochemical determinants of electrochemical polyelectrolyte multilayer swelling that are relevant to actuator usage. We used electrochemical quartz crystal microbalance with dissipation monitoring (EC-QCM-D) and cyclic voltammetry to compare the electrochemical swelling of two types of ferrocyanide-containing polyelectrolyte multilayers, poly(l-glutamic acid)/poly(allylamine hydrochloride) (PGA/PAH), and carboxymethyl cellulose/poly(diallyldimethylammonium chloride) (CMC/PDDA). We showed that ferrocyanide oxidation causes the swelling of PGA/PAH multilayers whereas it results in the contraction of CMC/PDDA multilayers. This behavior can be attributed to the presence of a positive and a negative Donnan potential in the case of PGA/PAH and CMC/PDDA multilayers, respectively. Using multilayers consisting of PGA and poly(allylamine) ferrocene (PGA/PAH-FC), we applied EC-QCM-D and demonstrated potentiostatic thickness control with nanometer precision and showed that the multilayer's thickness depends linearly on the applied potential within a certain potential range.

We investigated the thermodynamical properties of water exchanged in poly(l-glutamic acid)/poly(allylamine)hydrochloride (PGA/PAH) polyelectrolyte multilayers containing ferrocyanide. Oxidation/reduction of the ferrocyanide in the multilayer caused a reversible swelling/contraction of the film due to the uptake/release of counter ions and water. We used electrochemical quartz crystal microbalance and electrochemical microcalorimetry to correlate the amount of water with the accompanying entropy changes during electrochemical swelling of the multilayer for a series of different anions at different concentrations. The number of exchanged water molecules was highly dependent on the ionic strength and the type of anion in the buffer solution. However, the entropy change per exchanged water molecule was found to be independent of these two parameters. The water molecules in the polyelectrolyte multilayer have reduced the entropy compared to that of bulk water (≈-1 J mol(-1) K(-1)). A comparison of hydration entropies for free polyelectrolytes and PGA/PAH multilayers suggests that such systems are mainly stabilized by water release during multilayer construction.

We report that polyelectrolyte interdiffusion has a strong influence on the speed of electron transport in redox-active polyelectrolyte multilayers. For interdiffusive polyelectrolyte multilayers, the measured electron diffusion constants were consistently two orders of magnitude larger than the ones for systems where interdiffusion was not possible. This finding was verified for different polyelectrolyte multilayer systems that either allowed or prevented polyelectrolyte interdiffusion. The electron diffusion constants were deduced from cyclic voltammograms at various scanning speeds using the Randles–Sevcik equation for irreversible redox processes. The increased speed of electron transport in interdiffusive multilayers is explained by short-range movement of the redox-sites, allowing fast electron exchange through physical contact of neighboring redox-sites.