Amorphous Nanomaterial: Emerging Energy Storage Materials

Abstract

The accelerating impacts of climate change, combined with growing energy demands from artificial intelligence and the expansion of data centers, have created an urgent need for scalable and efficient battery technologies. Battery Energy Storage Systems (BESS) are critical for ensuring grid reliability, supporting renewable energy integration, and powering essential infrastructure. At the same time, the limited availability of lithium-ion batteries necessitates careful allocation toward applications that require both high energy density and power density. These include electric vehicles, medium- to heavy-duty trucks, delivery drones, and future aerial mobility vehicle such as eVTOLs. To meet the distinct needs of stationary and mobile storage, new material strategies are essential.This dissertation explores the use of amorphous nanomaterials to address key limitations in battery performance. Two case studies are presented. The first focuses on a non-stoichiometric sodium yttrium fluoride (NaYF-gel) developed as a fluoride-ion conducting electrolyte. The second investigates ultrasmall amorphous antimony sulfide nanoparticles as high-power-density negative electrode materials. In the first study, we synthesized a nanoporous NaYF-gel by reacting NaF and YCl3 in water at room temperature. The resulting ion-rich product consists primarily of amorphous YF3, which exhibits short-range structural motifs similar to the cubic phase of NaYF4. This gel gradually incorporates Na⁺ ions and eventually crystallizes into the fully stoichiometric phase NaYF4. To halt this crystallization, we applied flash freezing followed by lyophilization, yielding a powder with high surface area that can be redispersed in organic solvents to form a gel with enhanced fluoride-ion mobility. Electrochemical tests demonstrated reversible cycling with low polarization when paired with calcium fluoride and metal electrodes, including copper, lithium, and sodium. Spectroscopic analysis revealed that solvent coordination and moisture content critically influence ion mobility, providing new insights into the transport behavior of this system. In the second study, we developed a scalable room-temperature method to produce antimony sulfide nanoparticles smaller than 4 nm. These particles exhibited excellent performance in both Li-ion and Na-ion systems. The ligand environment during synthesis was found to influence both nanoparticle aggregation and electrochemical cycling behavior, despite being subsequently replaced with a different ligand. Replacing surface ligands or modifying coordination with molecules like trioctylphosphine altered its packing behavior and electrochemical performance. Compared to crystalline antimony, the amorphous form showed improved stability, which we attribute to reduced internal stress and possible thermodynamic factors. Pyrolysis of organic ligands created conductive carbon shells, further enhancing electrode conductivity. Together, these studies demonstrate the versatility of amorphous nanomaterials in improving transport properties, mechanical stability, and improved manufacturability. These findings support the continued development of tailored nanomaterials for next-generation battery systems across both stationary and mobile energy storage applications.