A homogenization study of the effects of cycling on the electronic conductivity of commercial lithium-ion battery cathodes

State-of-the-art image acquisition, image analysis, and modern homogenization theory are used to study the effects of cycling on commercial lithium-ion battery cathodes’ ability to conduct electronic current. This framework allows for a rigorous computation of an effective, or macroscale, electronic conductivity given an arbitrarily complicated three-dimensional microstructure comprised of three different material phases, i.e., active material, binder (polymer mixed with conductive carbon black), and electrolyte. The approach explicitly takes into account the geometry and is thus a vast improvement over the commonly used Bruggeman approximation. We apply our framework to two different types of lithium-ion battery cathodes before and after cycling. This leads us to predict an appreciable decrease in the effective electronic conductivity as a direct result of cycling. In addition, we present an ad-hoc “neighbor counting” methodology which meaningfully quantifies the effect of binder detaching from the surface of the active material due to the internal mechanical stresses experienced under operating conditions, thereby supporting the results of the homogenization calculations

The effect of ionic aggregates on the transport of charged species in lithium electrolyte solutions

In this investigation we focus on the problem of modelling the transport of the charged species (lithium ions) in electrolyte solutions with moderate and high salt concentrations (0.1M to >2M), and consider the Nernst-Planck equation as a model of such processes. First, using a combination of magnetic resonance imaging (MRI) and inverse modelling (IM) we demonstrate that at higher concentrations the Nernst- Planck equation requires negative transference numbers in order to accurately describe the concentration profiles obtained from experiments. The need for such a physically inconsistent constitutive relation indicates the loss of validity of the Nernst-Planck equation as a model for this process. Next we consider the formation of ion pairs and clusters as a possible effect responsible for the appearance of negative transference numbers and derive an extended version of the Nernst-Planck system which accounts for these additional species. However, a careful analysis of this model reveals that incorporation of ion-pairing effects into the modelling will not change the transference numbers inferred from the experimental data via inverse modelling. This demonstrates that physical effects other than formation of ion pairs and clusters must be incorporated into the Nernst-Planck model in order for it to correctly describe ion transport at higher salt concentrations. One prime candidate for such effects is the motion of the reaction surface resulting from dendrite growth

Use of cultivated plants and non-plant remedies for human and animal home-medication in Liuban district, Belarus

Background: To use any domestic remedy, specific knowledge and skills are required. Simple logic dictates that the use of wild plants in the context of limited interaction with nature requires prior identification, while in the case of non-plant remedies and cultivated plants this step can be omitted. This paper aims to document the current and past uses of non-plant remedies and cultivated plants in the study region for human/animal medication; to analyze the human medicinal and veterinary use areas in the context of the remedy groups; to qualitatively compare the results with relevant historical publications; and to compare the intensity and purpose of use between the remedy groups. Methods: During field studies 134 semi-structured interviews were conducted with locals from 11 villages in the LiubaÅ\u84 district of Belarus. Currently used home-remedies as well as those used in the past were documented by employing the folk history method. The subject was approached through health-related uses, not by way of remedies. Interview records were digitalized and structured in Detailed Use Records in order to ascertain local perceptions. An Informant Consensus Factor (FIC) was calculated for remedy groups as well as for different use categories. Results: In the human medication area the use of nearby remedies was neither very diverse nor numerous: 266 DUR for 45 taxa belonging to 27 families were recorded for cultivated plants along with 188 DUR for 58 different non-plant remedies. The FIC values for both remedy groups were lower than for wild plants. In the ethnoveterinary medicine use area there were 48 DUR referring to the use of 14 cultivated plant taxa from 12 families and 72 DUR referring to the use of 31 non-plant remedies. The FIC value for the whole veterinary use area of cultivated plants was relatively low, yet similar to the FIC of wild plants. Conclusions: Differences between remedy groups were pronounced, indicating that in domestic human medicine cultivated plants and non-plant remedies are either remarkably less important than wild ones or not considered worth talking about. In ethnoveterinary medicine non-plant remedies are almost equally important as wild plants, while cultivated plants are the least used. People in study area seem to still more often rely on, or are more willing to talk to strangers about, wild plants, as promoted by both official medicine and popular literature

Direct observation of ion dynamics in supercapacitor electrodes using in situ diffusion NMR spectroscopy

Ionic transport inside porous carbon electrodes underpins the storage of energy in supercapacitors and the rate at which they can charge and discharge, yet few studies have elucidated the materials properties that influence ion dynamics. Here we use in situ pulsed field gradient NMR spectroscopy to measure ionic diffusion in supercapacitors directly. We find that confinement in the nanoporous electrode structures decreases the effective self-diffusion coefficients of ions by over two orders of magnitude compared with neat electrolyte, and in-pore diffusion is modulated by changes in ion populations at the electrode/electrolyte interface during charging. Electrolyte concentration and carbon pore size distributions also affect in-pore diffusion and the movement of ions in and out of the nanopores. In light of our findings we propose that controlling the charging mechanism may allow the tuning of the energy and power performances of supercapacitors for a range of different applications