April 1-5, 2013 | San Francisco
Meeting Chairs: Mark L. Brongersma, Vladimir Matias, Rachel Segalman, Lonnie D. Shea, Heiji Watanabe
Silicon is an attractive high-capacity anode material for Li-ion batteries, but to design better-performing Si anodes, it is necessary to develop a comprehensive understanding of both the fundamental nature of the Li-Si reaction and the effects of silicon&’s ~300% volume change. Here, in situ transmission electron microscopy (TEM) is used to observe the reaction of crystalline Si nanoparticles in real time. The experiments reveal that the lithiation reaction slows dramatically as the reaction front progresses into particles of all sizes. Analysis of the reaction front trajectories suggests that the lithiation kinetics are not diffusion-controlled in the conventional sense, but that instead the reaction slows because large hydrostatic stresses in the vicinity of the reaction front diminish the driving force for the reaction. In addition, it was observed that in many cases, larger particles that fractured during lithiation were lithiated fully in a shorter time than smaller particles that did not fracture. This is attributed to stress relaxation that occurs during fracture, which results in faster reaction rates. Overall, our experimental results suggest that mechanical stress has a central role in governing the reaction kinetics in this unique large-volume change reaction. These findings inform our understanding of the rate performance of real Si anodes, and the observed dependence of reaction rate on size and fracture characteristics is important for designing optimized electrode architectures.
Performance of current Li-ion battery with liquid electrolytes is strongly dependent on the unique physical properties of the solid-electrolytes interphase (SEI) formed on the anode surface at the first-time charging. It has been known that th