We have performed a number of experiments to examine the mechanical behavior of high capacity anodes. In particular, using two separate techniques, we have measured the fracture energy of lithiated silicon thin-film electrodes as a function of lithium concentration. The fracture energy is found to be similar to that of pure silicon and essentially independent of the concentration of lithium. Thus, while lithiated silicon can flow plastically, it appears to fracture in a brittle manner. Additionally, we have measured stresses that develop during lithiation/delithiation of germanium electrodes. We have performed complementary XRD experiments to determine the phases that develop during lithiation/delithiation. These measurements demonstrate plastic flow in germanium, which limits the stresses, thus reducing the driving force for crack propagation. Overall, these experiments provide key insight into the development of high-capacity anode systems that avoid fracture and thereby enable long cycle life.
University of Illinois at Urbana-Champaign
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