Concentration Of Ionic Charge Carriers Research Articles

Locally Superconcentrated Electrolytes for Ultra-Fast-Charging Lithium Metal Batteries with High-Voltage Cathodes

Electric vehicles capable of recharging in the same time it takes to refuel a gasoline-powered car require electrolytes that maximize areal ion flux to enable electrochemical reactions to proceed at the same rate that current is passed through the external circuit. While strategies for increasing ionic charge carrier concentration in electrolytes are well-established, enhancements are made at the expense of carrier mobility, placing a ceiling on areal ion flux below the requirement for fast-charge. Here, we explore locally superconcentrated electrolytes, which employ a noncoordinating diluent to reduce viscosity, for delivering an 80% change in state-of-charge in Li|NMC622 batteries in 5–15 min. We investigate the effects of concentration, viscosity, ionic conductivity, and solvation on lowering fast-charge overpotentials and extending cycle life. We identify divergent failure mechanisms that occur on different time scales when cycling the cells at different charge rates and depths of discharge, which has implications for future electrolyte designs.

Light-Modulated Cationic and Anionic Transport across Protein Biopolymers*.

Light is a convenient source of energy and the heart of light-harvesting natural systems and devices. Here, we show light-modulation of both the chemical nature and ionic charge carrier concentration within a protein-based biopolymer that was covalently functionalized with photoacids or photobases. We explore the capability of the biopolymer-tethered photoacids and photobases to undergo excited-state proton transfer and capture, respectively. Electrical measurements show that both the photoacid- and photobase-functionalized biopolymers exhibit an impressive light-modulated increase in ionic conductivity. Whereas cationic protons are the charge carriers for the photoacid-functionalized biopolymer, water-derived anionic hydroxides are the suggested charge carriers for the photobase-functionalized biopolymer. Our work introduces a versatile toolbox to photomodulate both protons and hydroxides as charge carriers in polymers, which can be of interest for a variety of applications.

Light‐Modulated Cationic and Anionic Transport across Protein Biopolymers**

AbstractLight is a convenient source of energy and the heart of light‐harvesting natural systems and devices. Here, we show light‐modulation of both the chemical nature and ionic charge carrier concentration within a protein‐based biopolymer that was covalently functionalized with photoacids or photobases. We explore the capability of the biopolymer‐tethered photoacids and photobases to undergo excited‐state proton transfer and capture, respectively. Electrical measurements show that both the photoacid‐ and photobase‐functionalized biopolymers exhibit an impressive light‐modulated increase in ionic conductivity. Whereas cationic protons are the charge carriers for the photoacid‐functionalized biopolymer, water‐derived anionic hydroxides are the suggested charge carriers for the photobase‐functionalized biopolymer. Our work introduces a versatile toolbox to photomodulate both protons and hydroxides as charge carriers in polymers, which can be of interest for a variety of applications.

Electrical properties of electrochemically doped organic semiconductors using light-emitting electrochemical cells

We present a study of the electrical properties of electrochemically doped conjugated polymers using polymeric light-emitting electrochemical cells (PLECs) and interpreting the results according to a phenomenological model (PM) which assumes that, above the device turn-on voltage, the bulk transport properties of the doped organic semiconductor are responsible for the main contribution to the whole device conductivity. To confirm the predictions of this model, the dependence of the conductivity of PLECs with different parameters is evaluated and compared with the behavior expected for a doped semiconducting polymeric material. The organic semiconductor doping level, the blend concentration of organic semiconducting molecules, the device thickness, the charge carrier mobility, and the temperature are the parameters varied to perform this analysis. We observed that the device conductivity is independent of the active layer thickness, weakly dependent on the temperature, but strongly dependent on the semiconductor doping level, on the semiconductor fraction in the blend, and on the intrinsic charge carrier mobility. These results were well described by the variable range hopping (VRH) model, which has been widely employed to describe the charge transport in doped semiconducting polymeric materials, confirming the prediction of the phenomenological model. The current analysis demonstrates that PLECs are a suitable system for studying, in situ, the electrochemical doping of semiconducting polymers, permitting the evaluation of material properties as, for instance, the density of electronic charge carriers (and, consequently, the ionic charge carrier concentration) necessary to achieve the maximum electrochemical doping level of the organic semiconductor.

Studies on the structure and transport properties of hexanoyl chitosan-based polymer electrolytes

Polymer electrolytes composed of hexanoyl chitosan as the host polymer, lithium trifluoromethanesulfonate (LiCF 3 SO 3 ) as the salt, diethyl carbonate (DEC)/ethylene carbonate (EC) as the plasticizers were prepared and characterized by X-ray diffraction and impedance spectroscopy. The X-ray diffraction results reveal the variation in conductivity from structural aspect. This is reflected in terms of amorphous content. Sample with higher amorphous content exhibits higher conductivity. In order to further understand the source of the conductivity variation with varying plasticizers compositions as well as temperatures, the ionic charge carrier concentration and their mobility in polymer electrolyte were determined. The Rice and Roth model was proposed to be used to estimate the ionic charge carrier concentration, n . Knowing n and combining the result with dc conductivity, the mobility of the ionic charge carrier can be calculated. It is found that the conductivity change with DEC/EC composition is due mainly to the change in ionic charge carrier concentration while the conductivity change with temperature is due primarily to the change in mobility.

Time-of-flight ion mobility measurements in epoxy-amine systems during curing

The technique based on the time-of-flight (TOF) concept was proposed for determination of ion mobility in epoxy resins under isothermal curing conditions. This study extends our earlier investigations on this subject. Ionic conductivity dc measurements also were carried out in order to gain better understanding of the evolution of the ionic conductivity and mobility. The experiments have been performed for selected epoxy-amine systems that gellify and vitrify: diglycidyl ether of bisphenol A (DGEBA) with 4,4'-methylenebis [3-chloro-2,6-diethylaniline] (MCDEA) and for reacting medium that gellify only: diglycidyl ether of 1,4-butanediol (DGEBD) with 4,9-dioxa-1,12-dodecane diamine (4D). The differences found between the time dependency of the ionic conductivity and mobility during curing are explained by the decrease of the concentration of ionic charge carriers during the reaction. We conclude that the decrease of the ionic charge carrier density during the reaction, limits the applicability of the basic assumption of electrical techniques for reaction monitoring, that the ionic conductivity is related directly to the medium viscosity.

Charge carrier concentration and mobility of ions in a silica glass

Separate determination of the charge carrier concentration and the ionic mobility in glasses is difficult but useful in understanding the source of the conductivity variation in glasses with varying glass composition, cooling rates as well as temperatures. We suggest that the dielectric relaxation strength of the space charge polarization can be used to estimate the ionic charge carrier concentration and combining the result with dc conductivity, the ionic mobility can be determined. The method was used to determine the origin of the conductivity changes of a silica glass caused by fictive temperature change and water addition. We found that the observed conductivity decrease with increasing fictive temperature is due primarily to a decrease in mobility while the observed conductivity decrease with increasing water content is due primarily to a decrease in the charge carrier concentration.

Ionic space charge phenomena during SIMS analysis of ceramic materials

Despite recent progress in instrument design the surface analysis of poorly conducting materials by modern techniques operating with either primary and/or secondary charged particles always leads to an accumulation of electric charges on the bombarded surface. In materials with an appreciable ionic conductivity the resultant electric field will induce the migration of mobile species and will therefore modify elemental concentration profiles. As an illustration of this problem we present a phenomenological study of an ionic model material which contains only one mobile species (e.g. sodium or hydrogen in oxide glasses at room temperature). A simultaneous numerical solution of the diffusion equation and of Poisson's equation permits to calculate the electric field and the ionic charge carrier concentration profiles in the near surface region of the material as a function of time. Although material ablation by sputtering is not yet taken into account, this approach gives useful insights into what happens in the near surface region of an ionic conductor on analysing it by SIMS or related techniques which also produce shallow charged layers on the surface of the target. On the other hand, the results are also applicable to plasma based treatments of glass surfaces currently applied in PVD coating processes.