Xiaotang Lu: Synthesis and Application of Silicon-Based Nanomaterials

Xiaotang Lu began her Ph.D. studies in the Materials Science & Engineering Program in the Fall of 2011. She works on the synthesis and application of Silicon-based nanomaterials under the supervision of Dr. Brian Korgel.

Solution synthesis of nanomaterials has enjoyed great success due to milder experimental conditions compared to vacuum based techniques while maintaining excellent control over the morphology of the products. Xiaotang’s research focuses on the solution-based colloidal synthesis of one-dimensional semiconductor nanomaterials, e.g. Si and Ge nanowires and nanorods using both solution-liquid-solid (SLS) and supercritical fluid-liquid-solid (SFLS) growth mechanisms. In both mechanisms, the metal nanocrystals are employed to seed and promote the nanowires/nanorods crystallization: metal form eutectic or solid alloys with semiconductor at the beginning; the semiconductor precipitates one-dimensionally whenever it saturates in the seeds. Using these solution synthetic routes, large amount of high-quality crystalline Si and Ge nanostructures could be produced.

Si and Ge are promising candidates for replacing carbonaceous anodes in current lithium-ion batteries (LIBs) because they have much higher lithium storage density compared to the graphite (Si: 3579 mAh/g, Ge: 1362mAh/g, C:372 mAh/g). However, the massive volume change of Si, nearly 300%, upon lithiation/delithiation cycles pulverizes the material resulting in rapid capacity fade of the Si-based anode. Nanostructures have been shown to accommodate the dramatic structural evolution. Different nanostructures, such as nanowires, nanotubes, nanorods, and nanoparticles as well as Si-based nanocomposites, are being studied. Using in situ transmission electron microscope (TEM), the lithitation process can be visualized in real time providing direct information to better understand the electrochemical reaction in LIBs and the material degradation mechanism; helpful for understanding the failure mechanism of the anode and crucial for designing better nanostructures for high-performance LIBs.

Xiaotang’s work focuses on exploring the solution synthesis of Si and Ge nanomaterials and understanding the lithiation mechanism of these nanomaterials with assistance of in situ TEM. Her research goal is to develop an optimized nanostructure with high energy density and enhanced cyclability.

Modified SFLS growth of germanium nanowires and the scanning electron microscope (SEM) images of the nanowires.

Modified SFLS growth of germanium nanowires and the scanning electron microscope (SEM) images of the nanowires.

Sequential TEM images of in situ lithiation of the pyrolyzed Si nanowires (Red arrow indicates the lithiation front propagating along the nanowire).

Sequential TEM images of in situ lithiation of the pyrolyzed Si nanowires (Red arrow indicates the lithiation front propagating along the nanowire).