Bilash KC

I joined Dr. Klie’s nanoscience physics group (NSPG) in 2016. I am interested in developing model cathodes to study interfacial ion diffusion. I use Molecular Beam Epitaxy (MBE) to grow LiMn₂O₄ single crystal thin films which allows for atomically flat layers to be grown with well-defined surface terminations, orientations, defect concentrations and a homogenous distribution of compositional elements, which provides a good opportunity to characterize the cathodes in pristine and cycled states. The simplicity of single crystals compared to polycrystalline particulate cathode materials allows specific structural and chemical aspects of intercalation to be isolated and examined using nanoscale characterization techniques, such as transmission electron microscopy (TEM), scanning transmission electron microscopy (STEM), and electron energy loss spectroscopy (EELS), as well as more common X-ray diffraction (XRD), or X-ray photoemission spectroscopy (XPS). My ongoing research focuses on careful study of SEI layer, Li-ion diffusivity, and understanding of structural framework changes in cycled cathodes to improve cyclability and capacity retention.

B.S., Physics, McNeese State University (2012)
Ph.D. candidate, Physics, University of Illinois at Chicago (2014-)

Li-ion batteries, the current paradigm of electrochemical energy storage technologies, face increasing demands for large-volume production of highly efficient and stable devices. The search for new cathode materials that can intercalate Li-ions more efficiently and at higher reversible concentrations is still a highly active research area, with considerable interest on lithium transition metal oxides, such as LiMn₂O₄. However, due to high reactivity of Lithium, LiMn₂O₄ are generally synthesized by methods such as PLD, sputtering, sol-gel etc. which generally results in powdered or polycrystalline samples making detailed study of surfaces and interfaces difficult. In contrast, our MBE grown films allow desired calibration of elemental lithium and manganese flux which yield well-defined surface terminations, orientations, defect concentrations, and a homogenous distribution of compositional elements. We adjust elemental flux rate, oxygen partial pressure, and growth temperature under ultra-high vacuum(UHV) environment to obtain highly crystalline LiMn₂O₄ films. Once the films are grown, we assemble them into coin cells under inert atmosphere, and perform electrochemical tests. The samples are assembled, transferred and stored in argon filled container/box to preserve the structural quality over a long period of time. We do structural and chemical characterization using TEM, aberration-corrected STEM, energy-dispersive X-ray spectroscopy (EDS), EELS, as well as XRD and XPS for comparison to conventional electrochemical systems. We analyze the pristine and cycled films, and examine the structural and chemical changes such as of SEI layer formation, Li-ion diffusivity, valence change, structural distortion etc. We also grow different orientations of films to understand the oriented dependent properties of films on all our experiments.

Our work will shed further light on the complex surface reaction mechanisms associated with LiMn₂O₄ cathode.