Ran Elazari

Challenges in the development of advanced Li-ion batteries: a review

Li-ion battery technology has become very important in recent years as these batteries show great promise as power sources that can lead us to the electric vehicle (EV) revolution. The development of new materials for Li-ion batteries is the focus of research in prominent groups in the field of materials science throughout the world. Li-ion batteries can be considered to be the most impressive success story of modern electrochemistry in the last two decades. They power most of todays portable devices, and seem to overcome the psychological barriers against the use of such high energy density devices on a larger scale for more demanding applications, such as EV. Since this field is advancing rapidly and attracting an increasing number of researchers, it is important to provide current and timely updates of this constantly changing technology. In this review, we describe the key aspects of Li-ion batteries: the basic science behind their operation, the most relevant components, anodes, cathodes, electrolyte solutions, as well as important future directions for R&D of advanced Li-ion batteries for demanding use, such as EV and load-leveling applications.

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.

Sulfur‐Impregnated Activated Carbon Fiber Cloth as a Binder‐Free Cathode for Rechargeable Li‐S Batteries

A route for the preparation of binder-free sulfur-carbon cathodes is developed for lithium sulfur batteries. The method is based on the impregnation of elemental sulfur into the micropores of activated carbon fibers. These electrodes demonstrate good electrochemical performance at high current density attributed to the uniform dispersion of sulfur inside the carbon fiber.

Morphological and Structural Studies of Composite Sulfur Electrodes upon Cycling by HRTEM, AFM and Raman Spectroscopy

In this work, structural and morphological changes in composite sulfur electrodes were studied due to their cycling in rechargeable Li-S cells produced by Sion Power Inc. Composite sulfur cathodes, comprising initially elemental sulfur and carbon, undergo pronounced structural and morphological changes during discharge-charge cycles due to the complicated redox behavior of sulfur in nonaqueous electrolyte solutions that contain Li ions. Nevertheless, Li―S cells can demonstrate prolonged cycling. To advance this technology, it is highly important to understand the evolution of the structure and morphology of sulfur cathodes as cycling proceeds. High resolution scanning and tunneling microscopy, scanning probe microscopy, and Raman spectroscopy were used in conjunction with the electrochemical measurements. A special methodology for slicing composite sulfur electrodes and their cross sectioning and depth profiling was developed. The gradual changes in the structure of sulfur cathodes due to cycling is described and discussed herein. Important phenomena include changes in the surface electrical conductivity of sulfur electrodes and pronounced morphological changes due to the irreversibility of the sulfur redox reactions. Based on the observations presented in this work, it may be possible to outline guidelines for improving Li-S battery technology and extending its cycle life.

The Use of Redox Mediators for Enhancing Utilization of Li2S Cathodes for Advanced Li–S Battery Systems

The development of Li2S electrodes is a crucial step toward industrial manufacturing of Li-S batteries, a promising alternative to Li-ion batteries due to their projected two times higher specific capacity. However, the high voltages needed to activate Li2S electrodes, and the consequent electrolyte solution degradation, represent the main challenge. We present a novel concept that could make feasible the widespread application of Li2S electrodes for Li-S cell assembly. In this concept, the addition of redox mediators as additives to the standard electrolyte solution allows us to recover most of Li2S theoretical capacity in the activation cycle at potentials as low as 2.9 VLi, substantially lower than the typical potentials >4 VLi needed with standard electrolyte solution. Those novel additives permit us to preserve the electrolyte solution from being degraded, allowing us to achieve capacity as high as 500 mAhg(-1)Li2S after 150 cycles with no major structural optimization of the electrodes.

Assessing the Solvation Numbers of Electrolytic Ions Confined in Carbon Nanopores under Dynamic Charging Conditions.

We propose herein a new reliable approach to assess solvation numbers of ions confined in carbon nanopores based on dynamic quartz crystal measurements. This was proved for the entire families of alkaline, alkaline-earth cations, and halogen anions. As-assessed hydration numbers appear in the sequence characteristic of a transition from the cosmotropic to a chaotropic-type behavior with the decrease of the ions charge-to-size ratio. The information on the behavior of ions confined in nanometric space of different (especially charged) carbon materials is in high demand for the development of powerful supercapacitors, nanofiltration membranes, and chemical/biochemical sensors.