Hyeongjun Koh

Graphite plays an essential role in energy storage and electrochemical applications; however, the reliance on mining and petroleum-derived precursors in conventional graphite manufacturing presents environmental and economic challenges. Biomass offers a renewable and widely available alternative feedstock for synthetic graphite production. In this study, we explore the graphitization of cellulose as a model biomass precursor, focusing on how graphitization heating conditions influence microstructural evolution and electrochemical behavior. Using rapid Joule heating and conventional thermal treatments, we characterize the resulting biocarbon materials with respect to their crystallinity, grain size, and morphology. Electrochemical testing reveals that heating rate and duration significantly impact capacity retention and rate performance, with faster heating producing smaller grain sizes and improved high-rate capabilities. These findings demonstrate a direct link between processing conditions and electrochemical performance, highlighting biomass-derived graphite as a viable pathway toward distributed graphite production.

Large-scale battery manufacturing requires understanding the fundamental principles of materials and interfaces and relies on advanced techniques for detailed interrogation. Despite advancements in the industrial scale production and their associated quality control tools, challenges such as electrode heterogeneity, internal defects, and large-scale material waste (e.g., scrap) can hamper manufacturing. Synchrotron X-ray characterization techniques offer spatial, temporal, and chemical resolution that can provide diagnostic insights for metrology across various manufacturing steps. This review examines the use of synchrotron tools to advance understanding of key steps in the battery manufacturing process. Recent examples demonstrate how synchrotron methods resolve manufacturing challenges and uncover degradation pathways that are otherwise inaccessible. Future directions for advancing battery manufacturing emphasize collaboration between academia and industry through the use of synchrotron X-ray techniques.

An environmentally responsible synthesis of Na_2/3[Ni_1/3Mn_2/3]O₂ (NNMO) enabled by direct conversion of metallic Ni powder, releasing only O₂ and H₂O as byproducts. The resulting NNMO exhibits excellent cycling performance as a Na-ion battery cathode.

It is essential to understand the nanoscale structure and chemistry of energy storage materials due to their profound impact on battery performance. However, it is often challenging to characterize them at high resolution, as they are often fundamentally altered by sample preparation methods. Here, we use the cryogenic lift-out technique in a plasma-focused ion beam (PFIB)/scanning electron microscope (SEM) to prepare air-sensitive lithium metal to understand ion-beam damage during sample preparation. Through the use of cryogenic transmission electron microscopy, we find that lithium was not damaged by ion-beam milling although lithium oxide shells form in the PFIB/SEM chamber, as evidenced by diffraction information from cryogenic lift-out lithium lamellae prepared at two different thicknesses (130 and 225 nm). Cryogenic energy loss spectroscopy further confirms that lithium was oxidized during the process of sample preparation. The Ellingham diagram suggests that lithium can react with trace oxygen gas in the FIB/SEM chamber at cryogenic temperatures, and we show that liquid oxygen does not contribute to the oxidation of lithium process. Our results suggest the importance of understanding how cryogenic lift-out sample preparation has an impact on the high-resolution characterization of reactive battery materials.