Section: New Research Projects

Molecularly Designed Architectures for High Energy Density Li/S Batteries

PI Team members include: Héctor Abruña, Lynden Archer, Geoffrey Coates, Emmanuel Giannelis, Richard Hennig and Ulrich Wiesner.

Electrical energy storage (EES) in the form of secondary/rechargeable batteries and supercapacitors is key to developing mobile electricity-powered devices ranging from consumer electronics to electrified vehicles. EES will also be of great importance in residential/stationary and grid applications as well as enable energy capture from intermittent renewable sources [1]. These and other applications require electrical energy supplies that maintain exceptional performance throughout long-term, intense use. Successful development of new batteries for these applications hinges on the discovery of high energy density electroactive materials capable of reversibly storing/releasing electrical energy at fast charge/discharge "C" rates. The batteries must also be safe to operate and prepared from abundant and inexpensive materials. Individually, these requirements are challenging; collectively they are daunting.

With a capacity of 1,675 mAh/g and an energy density of about 2,600 Wh/kg, the lithium/sulfur (Li/S) system has been considered one of the most attractive platforms for developing high-energy secondary batteries. Despite intensive research efforts by research teams world-wide, the development of practical batteries approaching its high theoretical performance has proven elusive [2-4]. This is due, at least in part, to a lack of a fundamental understanding of the mechanistic details of the processes that accompany the charge/discharge events for sulfur as a cathode material. For example, the redox chemistry of sulfur is very solvent dependent with "traditional" battery solvents such as the organic carbonates providing very poor performance while ethereal solvents (i.e. glymes) exhibit much better performance. This example reflects a generally understood fact that tried-and-true approaches from other battery platforms cannot be directly adapted to the Li/S system. Additionally, the use of metallic lithium in the Li/S battery, while seductively attractive due to its extremely high theoretical capacity, presents critical safety concerns due to dendrite formation after many charge/discharge cycles, which often results in penetration of the separator and shorting with potentially catastrophic consequences.

All of these aspects reflect materials' limitations. Thus, it is clear that if the objective is to develop a high performance rechargeable battery based on the Li/S system, a balanced approach that embraces fundamental understanding of the various processes involved as well as the discovery and development of new materials systems is required.