(Invited) From Lithiated Transition Metal Oxide to Silicon and Lithium-Sulfur Systems: An Evolution of Electrochemically Active Materials (2022)

Energy storage is vital for driving an energy independent world economy that is currently largely dependent on exploiting natural reserves supplemented by oil and gas exports. The field of Li-ion batteries continues to witness burgeoning progress since the commercialization of the first Li-ion battery (LIB) by Sony in 1991, and is at present, clearly the flagship rechargeable battery system. Correspondingly, enormous progress is seen in cathodes, electrolytes as well as anodes [1]. New materials have continuously evolved. Lithiated transition metal oxides despite advances in various systems, are still the flagship cathodes of choice relying on ubiquitous intercalation chemistries. Newer chemistries exploiting alloying and Zintl phase formation focusing on silicon and tin as alternative anodes have also evolved in the last two decades. Similarly, there is tremendous research in the area of alternative energy storage systems beyond lithium-ion intercalation chemistry. Lithium-sulfur batteries (LSB) and Li metal anodes have putatively emerged at the forefront and are the spotlight of increased research activity in recent years. All these systems are unfortunately, plagued by intransigent inferior electronic conductivity, Li-ion conductivity, voltage-specific phase transition related kinetic limitations accompanied with ensuing chemical, physical, and electrochemical challenges. Nano-engineered approaches aided by concomitant progress in science and technology of synthetic and analytical chemistry of advanced materials appear primed for overcoming these hurdles. We initiated work introducing solution-based chemical synthesis strategies for generating nanostructured lithiated transition metal oxides, including anti-site defect-free LiNiO 2 [2,3]. This work then transitioned into alternative anodes[4] and presently into the Li-S systems holding much promise, albeit major challenges remain to be overcome. 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 silicon nanotubes (h-SiNTs), cost-effective template derived nanoscale morphologies, scribable and flexible hetero-structured Si architectures, displaying impressive capacities of ~3000 mAh/g with sustained cyclability and high-rate capability in Si anodes [4]. Electrochemical approaches were also developed creating binder-less Si-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 conductors (LIC) coupled with chemically linked complex framework materials (CFM) based matrices for encapsulating S along with novel fine yarn-like and tethered S architectures yielding 5.5 mAh/cm 2 – 12 mAh/cm 2 areal capacity and ~1200 mAh/g specific capacity with S loadings as high as 20 mg/cm 2 displaying ~250 cycles cycling stability [5, 6]. Single layer pouch cells exhibiting 180-200 Wh/kg were also demonstrated. Developing scalable economic approaches, however, remain a key challenge. Engineering strategies were also developed for identifying new Li metal alloy anodes preventing and eliminating dendrite formation. These systems serve as alternative safe anodes to Li metal. This presentation will thus provide an overview of the above systems. Similarly, insights into the promising future in generating tailored functional engineered systems in the rapidly evolving digitally savvy era of the 21 st century will also be presented. Finally, the prospects of these systems offering a pathway to potentially achieving energy independence in the near future will also be outlined. References Wang, P.N. Kumta, et al. ACS Nano (2011). C-C. Chang, P.N. Kumta et al. J. Electrochemical Society 147 (2000). C. Chang, P.N. Kumta et al. J. Power Sources 75 (1998). Gattu, P.N. Kumta et al. Nano Research (2017). M. Shanthi, P.N. Kumta et al. Electrochimica Acta (2017). M. Shanthi, P.N. Kumta et al. Applied Energy Materials (2018).