Mass transport in the electrolyte is one of the limiting processes when it comes to the power density and energy efficiency of lithium-ion batteries. Electrolyte characterizations are therefore of utmost importance. This study reports the ionic conductivity, diffusion coefficient, lithium-ion transport number, and thermodynamic enhancement factor, as well as density and viscosity, for the electrolyte LiPF 6 in EC:DEC (1:1, by weight) at 10 • C, 25 • C, and 40 • C and for concentrations between 0.5 M and 1.5 M. By combining mathematical modeling and three experiments: conductivity measurements, concentration cells, and galvanostatic polarizations, the mass transport phenomena were fully characterized. All parameters were found to vary strongly with both concentration and temperature proving that temperature dependent parameters are essential when studying thermal behavior of lithium-ion batteries. Moreover, conductivity increased with temperature and showed a local maximum at around 1 M within the concentration range at all temperatures. The other parameters either showed a continuous decrease (diffusion coefficient and lithiumion transport number) or increase (thermodynamic enhancement factor) with concentration at all temperatures. Limited liquid range leading to solvent crystallization at 10 • C leads to very poor performance, possibly due to the strong coordination between the lithium ion and the crystallizing species, EC. Overall, the studied electrolyte is found to perform poorly compared to previously studied systems.Lithium-ion batteries (LIBs) have proven their commercial viability by conquering most markets for rechargeable batteries, including mobile devices and electric vehicles. The high power performance of LIBs has been found to be limited by the transport of lithium ions in the electrolyte. 1-4 As these batteries are being implemented in increasingly demanding applications, such as hybrid electric vehicles, an accurate prediction of their performance is crucial, to be able to design better battery packs. The predictions are made possible through modeling, which requires characterization of the mass-transport properties of the materials used in a wide range of operational conditions, including variations in temperature.Characterizations of electrolytes are not uncommon. However, they are mostly limited to partial investigations, providing only some of the properties needed to describe the performance of the electrolyte or assuming that it behaves like a dilute system (or both). 5,6 Concentrated electrolyte theory, which includes ion-ion interactions by implementing friction coefficients for all components, 7 should be used when modeling and characterizing the electrolytes used in LIBs, as dilute theory will generate big deviations in concentration profile simulation, and in extension voltage prediction, especially at high currents.

Our experiments with IEEE 802.11b based wireless ad hoc networks show that neighbor sensing with broadcast messages introduces "communication gray zones": in such zones data messages cannot be exchanged although the HELLO messages indicate neighbor reachability. This leads to a systematic mismatch between the route state and the real world connectivity, resulting in disruptive behavior for some ad hoc routing protocols. Concentrating on AODV we explore this issue and evaluate three different techniques to overcome the gray zone problem. We present quantitative measurements of these improvements and discuss the consequences for ad hoc routing protocols and their implementations.

We have built an Ad hoc Protocol Evaluation testbed (APE) in order to perform large-scale, reproducible experiments. APE aims at assessing several different routing protocols in a real world environment instead of by simulation. We present the APE testbed architecture and report on initial experiments with up to 37 physical nodes that show the reproducibility and scalability of our approach. Several scenario scripts have been written that include strict choreographic instructions to the testers who walk around with ORiNOCO equipped laptops. We introduce a metric called Virtual Mobility that we use to compare different testruns. This metric is based on the measured signal quality instead of the geometric distance between nodes, hence it reflects how a routing protocol actually perceives the network's dynamics.

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Superconcentration of aprotic electrolytes has recently emerged as a way to stabilize solvents that otherwise would be impossible to use, in e.g. lithium-ion batteries (LIBs). As demanding applications, such as hybrid electric vehicles and fast charging, become increasingly important, battery manufacturers are struggling to find a suitable electrolyte able to deliver high power with low polarization. Electrolyte characterizations able to accurately predict the high-power performance of such electrolytes are also of utmost importance. This study reports a full characterization of the mass-transport phenomena for a superconcentrated LiTFSI:acetonitrile electrolyte in concentrations ranging from 2.7 M to 4.2 M. The method obtains the ionic conductivity, cationic transport number, diffusion coefficient, and the thermodynamic enhancement factor, by combining mathematical modeling and three electrochemical experiments. Furthermore, the density and the viscosity were measured. The transport number with respect to the room is found to be very high compared to other liquid LIB electrolytes, but a low diffusion coefficient lowers overall performance. The ionic conductivity decreases quickly with concentration, dropping from 12.7 mS/cm at 2.7 M to 0.76 mS/cm at 4.2 M. Considering all the effects in terms of the mass-transport of the electrolyte, the lower end of the studied concentration range is favorable.Ethylene carbonate has long been regarded as a mandatory component in lithium-ion batteries (LIBs), because of its ability to form a stable solid-electrolyte interphase on graphite electrodes. 1 However, Yamada et al. recently showed that salt superconcentration (>3 M), the "solvent in salt" concept, stabilizes solvents that would otherwise not provide reversible performance. 2-7 In particular, they showed that they could improve reversibility of LIBs with electrolytes containing dimethyl sulfoxide (DMSO), 1,2-dimethoxyethane (DME), 1,2-dioxolane (DOL), acetonitrile (ACN), and tetrahydrofuran (THF) by using superconcentrated solutions of lithium (Li) bis(fluorosulfonyl)imide (FSI) or Li bis(trifluoromethanesulfonyl)imide (TFSI). The improved stability is believed to be due to the fact that all the solvent molecules are coordinated to the salt, i.e. there are no "free" solvent molecules, thus preventing destructive solvent co-intercalation into graphite. 5,8 The characterization and evaluation of these superconcentrated electrolytes has mainly been done by cycling tests using either lithium metal/graphite half-cells, or physical methods such as Raman spectroscopy, and viscosity measurements. The only electrochemical properties reported are the ionic conductivity, 3,7,9 and the lithium-ion transport number, 7 using a method that has been proven not be applicable even at the concentrations used in normal electrolytes. 10 However, the cycling tests indicate that the superconcentrated electrolytes have very promising performance with a reversible capacity surpassing that of carbonate electrolytes and a much improved high-rate ...

Our experiments with IEEE 802.11b based wireless ad hoc networks show that neighbor sensing with broadcast messages introduces "communication gray zones": in such zones data messages cannot be exchanged although the HELLO messages indicate neighbor reachability. This leads to a systematic mismatch between the route state and the real world connectivity, resulting in disruptive behavior. Concentrating on AODV we explore this issue and present three different techniques to overcome the gray zone problem.

No abstract

Thermal effects are linked to all main barriers to the widespread commercialization of lithium-ion battery powered vehicles. This paper presents a coupled 2D electrochemical – 3D thermal model of a large-format prismatic lithium-ion battery, including a thermal management system with a heat sink connected to the surface opposite the terminals, undergoing the dynamic current behavior of a plug-in hybrid electric (PHEV) vehicle using a load cycle with a maximum current of 8 C, validated using potential and temperature data. The model fits the data well, with small deviations at the most demanding parts of the cycle. The maximum temperature increase and temperature difference of the jellyroll is found to be 9.7°C and 3.6°C, respectively. The electrolyte is found to limit the performance during the high-current pulses, as the concentration reaches extreme values, leading to a very uneven current distribution. Two other thermal management strategies, short side and long side surfaces cooling, are evaluated but are found to have only minor effects on the temperature of the jellyroll, with maximum jellyroll temperatures increases of 9.4°C and 8.1°C, respectively, and maximum temperature differences of 3.7°C and 5.0°C, respectively.