Elad Pollak

On the Surface Chemical Aspects of Very High Energy Density, Rechargeable Li–Sulfur Batteries

Li(metal)-sulfur (Li-S) systems are among the rechargeable batteries of the highest possible energy density due to the high capacity of both electrodes. The surface chemistry developed on Li electrodes in electrolyte solutions for Li-S batteries was rigorously studied using Fourier transform infrared and X-ray photoelectron spectroscopies. A special methodology was developed for handling the highly reactive Li samples. It was possible to analyze the contribution of solvents such as 1-3 dioxolane, the electrolyte LiN(SO 2 CF 3 ) 2 , polysulfide (Li 2 S n ), and LiNO 3 additives to protective surface films that are formed on the Li electrodes. The role of LiNO 3 as a critical component whose presence in solutions prevents a shuttle mechanism that limits the capacity of the sulfur electrodes is discussed and explained herein.

Electrolyte Solutions with a Wide Electrochemical Window for Rechargeable Magnesium Batteries

Electrolyte solutions for rechargeable Mg batteries were developed, based on reaction products of phenyl magnesium chloride (PhMgCl) Lewis base and Alcl 3 Lewis acid in ethers. The transmetallation of these ligands forms solutions with Mg x Cl + y and AlCl 4-n Ph n - ions as the major ionic species, as analyzed by multinuclei nuclear magnetic resonance spectroscopy. Tetrahydrofuran (THF) solutions of (PhMgCl) 2 -Alcl 3 exhibit optimal properties: highly reversible Mg deposition (100% cycling efficiency) with low overvoltage: <0.2 V and electrochemical windows wider than 3 V. A specific conductivity of 2-5 X 10 -3 Ω -1 cm -1 could be measured between -10 and 30°C for these solutions, similar to that of standard electrolyte solutions for Li batteries. Mg ions intercalate reversibly with Chevrel phase (Mg x Mo 6 S 8 ) cathodes in these solutions. These systems exhibit high thermal stability. The solutions may enable the use of high voltage, high-capacity Mg insertion materials as cathodes and hence open the door for research and development of high-energy density, rechargeable Mg batteries.

Review on Engineering and Characterization of Activated Carbon Electrodes for Electrochemical Double Layer Capacitors and Separation Processes

Carbonaceous materials are highly important electrode materials due to their wide electrochemical window, inertness with a wide spectrum of electroactive materials, and the possibility to develop highly porous but yet conductive activated carbons. Carbon cloth electrodes could be prepared from simple polymeric materials such as cotton cloth (poly-cellulose) and then could be activated by mild oxidation processes (e.g., using CO2 at elevated temperatures). Monolithic, conductive carbon cloth electrodes with specific surface area up to 2000 m2/g could be obtained and their porosity could be adjusted by the activation process and calibrated by adsorption processes from both gas and solution phases. Capacities up to 350 F/g could be obtained with activated carbon electrodes in acidic aqueous solutions, which makes these systems very promising for super-capacitor devices. Highly interesting are the correlations between electro-adsorption processes and the electrical properties of activated carbon electrodes, as described herein. This review provides useful guidelines for the engineering of porous carbon electrodes and their characterization by electrochemical, spectral, and physical methods.