(Invited) Strategies for Achieving High-Energy Density Storage Systems
Authors: Kumta Prashant Nagesh 
Published: February 2020

Energy storage is vital for driving an energy independent world economy currently largely dependent on exploiting natural reserves supplemented by oil and gas exports. The field of Li-ion batteries has witnessed tremendous progress since the commercialization of the first Li-ion battery (LIB) by Sony in 1991. Correspondingly, there has been tremendous progress in the areas of cathode, electrolytes as well as anodes [1]. The area of lithiated transition metal oxides despite much advances, are still the flagship cathode systems largely focused on intercalation chemistry. However, the last two decades witnessed exploration of newer chemistries exploiting alloying and zintl phase formation focusing on silicon and tin as alternative anodes. Similarly, there has been tremendous research in the area of alternative energy storage systems beyond lithium-ion intercalation chemistry. Lithium-sulfur batteries (LSB) and Li metal anodes have accordingly emerged in the forefront and have been the spotlight of much research activity in recent years. All the systems are unfortunately, plagued by intransigent inferior electronic conductivity and voltage-specific phase transition related kinetic limitations accompanied with ensuing chemical, physical, and electrochemical challenges. Nano-engineered approaches coupled with the concomitant progress made in science and technology of synthetic and analytical materials chemistry appear primed for overcoming these hurdles.

We have thus far, implemented dynamic theoretical and experimental strategies to develop 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. Additionally, we have developed several approaches utilizing nanoscale droplets, nanoparticles, hollow Si nanotubes (h-SiNTs), cost-effective template derived nanoscale morphologies, scribable and flexible hetero-structured architectures displaying impressive capacities as high as ~3000 mAh/g with sustained cyclability and high rate capability in Si anodes[2]. Electrochemical approaches have also been developed for generating binder-less silicon based thin film anodes with considerable promise. Similarly, engineering approaches were implemented for generating sulfur cathodes in LSBs exploiting the tailored attributes of inorganic, nanocomposite, tethered, and polymeric lithium ion conducting (LIC) coupled with chemical framework materials (CFM) based matrices for encapsulating sulfur along with novel fine yarn-like and tethered architectures yielding 5.5 mAh/cm2 – 12 mAh/cm2 areal capacity as well as ~1200 mAh/g specific capacity with sulfur loadings as high as 20 mg/cm2 displaying up to 250 cycles cycling stability [3, 4]. New materials were identified serving as novel dendrite free anodes. Engineering strategies were also developed for stabilizing the Li metal anodes preventing and eliminating dendrite formation. These systems together have been studied as alternative safe anodes to the currently used Li metal anodes. Results of these studies will be presented and discussed. The presentation will also provide an insight into the promising future in store for generating tailored functional engineered systems in the rapidly evolving digitally savvy era of the 21st century as a pathway to potentially achieving energy independence in the near future.

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M. Shanthi, P.N. Kumta et al. Applied Energy Materials (2018)