(Invited) Opportunities and Challenges for Achieving High Performance Electrochemically Active Systems

Abstract

Energy storage and conversion are critical for meeting the growing energy demands of the increasing global population. Current energy demands are still largely met by exploiting natural reserves supplemented by oil and gas exports. Energy storage is dominated by the ubiquitously popular Li-ion battery technology which has witnessed tremendous progress attaining the flag ship technology status since the commercialization of the first Li-ion battery (LIB) by Sony in 1991. Correspondingly, the system has seen unbridled progress in all areas of cathode, electrolytes and anodes [1]. Lithiated transition metal oxides exploiting a combination of Ni, Mn and Co with higher Ni contents have been the subject of much intense activity of late. The last two decades heralded new alloying chemistry of zintl phases focused on silicon and tin as alternative anodes offering almost 10-fold higher specific capacity than conventional graphite. Pursuit of higher energy density systems triggered much research and interest in the areas of alternative energy storage systems beyond lithium-ion intercalation chemistry. Correspondingly, lithium-sulfur batteries (LSB) and dendrite free Li metal anodes (LMA) have surged into the forefront as promising next generation systems. All these systems are however, plagued by intractable inferior electronic conductivity, particularly, polysulfide dissolution in the former and voltage-specific phase transitions related kinetic limitations accompanied with ensuing chemical, physical, and electrochemical challenges. Nano-engineered and nano-scale directed approaches coupled with the concomitant developments in science and technology of synthetic and analytical materials chemistry have shown much promise for overcoming these limitations in recent years. Similarly, the field of electrocatalysis for proton exchange membrane (PEM) based water electrolysis has seen a surge of activity for driving the much touted hydrogen economy. Generation of precious group metal (PGM) free electrocatalysts has been the Holy Grail. We have thus far, implemented dynamic theoretical and experimental strategies to develop new engineered electronic and Li-ion conducting nanomaterials showing considerable promise as supporting components augmenting the performance and overcoming many of the limitations affecting these systems. We have thus developed flexible hetero-structured Si anode based architectures displaying impressive capacities as high as ~3000 mAh/g with sustained cyclability and high rate capability [2]. Electrochemical approaches have also been developed for generating binder-less silicon based composite anode structures with considerable promise overcoming the first cycle irreversible (FIR) loss without loss in capacity. Similarly, engineered strategies were developed for generating novel sulfur based cathodes in LSBs exploiting the nanostructured attributes of inorganic and organic, nanocomposite, tethered, and polymeric lithium ion conducting (LIC) coupled with chemical framework materials (CFM) based matrices for encapsulating sulfur along with novel 3D printed composite layered and tethered architectures yielding 5.5 mAh/cm2 – 12 mAh/cm2 areal capacity with sulfur loadings as high as 20 mg/cm2 displaying up to 250 cycles cycling stability [3, 4]. Similarly new novel dendrite free anode systems were also identified. Engineering strategies were thus developed for stabilizing the Li metal anodes preventing and eliminating dendrite formation. These systems together are targeted as safe anodes to the currently used Li metal anodes. Finally, efforts have focused on identifying new PGM-free electrocatalysts for acid mediated oxygen evolution reaction[5]. Results of these studies will be presented and discussed. Finally, insights into the future of functional engineered systems as a pathway to an energy independent future will also be discussed.