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Influence of Mechanical Loading on the Integrity and Performance of Energy Harvesting and Storage Materials at the Micron and Submicron Scales

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Technical Report,15 Jun 2012,14 Dec 2015

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U. Illinois at Urbana-Champaign Urbana United States

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The mechanical reliability and efficiency of thin film photovoltaics attached to structural members depends on the initial residual stresses in the films. In this research, accurate predictions of the mechanical and functional failure of photovoltaic films co-cured on carbon fiber composite laminates were made possible by quantifying the mean and gradient residual stresses and the failure properties of individual layers in thin film amorphous Si photovoltaics. The experimental results were employed to predict the onset of fragmentation in the transparent conductive oxide ZnO layer and the amorphous Si and the initiation of functional degradation of photovoltaic films co-cured on 0 degrees carbon fiber composite laminates. In parallel, this research program investigated the electrochemical and mechanical performance of graphite and Sn composite anodes subjected to electrochemical cycling. Most composite anodes reported in literature are very porous because they are manufactured from slurry, and as a result, they have no mechanical integrity. The composite graphite and Sn anodes fabricated in this research were prepared by hot pressing which allowed for control of their porosity between 35 and 75. Porosities larger than 45 preserved the electrochemical capacity of the anodes, as opposed to those with porosities smaller than 40 that had reduced electrochemical capacity. Graphite anodes with 45 porosity demonstrated the highest retention of tensile strength and elastic modulus after 30 electrochemical cycles, representing an optimum condition. Finally, the fracture of Si as high capacity Li host material was investigated using Si microsprings. Experiments conducted under purely chemical lithiation, showed good lithiation and small propensity for crack formation, thus making films of such springs a viable material for high capacity thin film anodes.

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