Silicon-graphite electrodes usually exhibit improved cycling stability when limiting the capacity exchanged by the silicon particles per cycle. Yet, the influence of the upper and the lower cutoff potential was repeatedly shown to differ significantly. In the present study, we address this discrepancy by investigating two distinct degradation phenomena occurring in silicon-graphite electrodes, namely (i) the roughening of the silicon particles upon repeated (de-)lithiation which leads to increased irreversible capacity losses, and (ii) the decay in the reversible capacity which mainly originates from increased electronic interparticle resistances between the silicon particles. First, we investigate the cycling stability and polarization of the silicon-graphite electrodes in dependence on different cutoff potentials using pseudo full-cells with capacitively oversized LiFePO 4 cathodes. Further, we characterize postmortem the morphological changes of the silicon nanoparticles by means of scanning transmission electron microscopy (STEM) and energy dispersive spectroscopy (EDS) as a function of the cycle number. To evaluate the degradation of the entire electrode coating, we finally complement our investigation by impedance spectroscopy (EIS) with a gold-wire micro-reference electrode and post-mortem analyses of the electrode structure and coating thickness by cross-sectional SEM. Silicon is among the most promising anode materials for future lithium-ion batteries.1,2 For example, a prismatic hard case cell comprising a silicon-carbon anode with 1000 mAh gand an NMC811 cathode would offer a specific energy of up to ∼280 Wh kgcell . 3 In contrast to state-of-the-art graphite electrodes, where lithium is inserted into the interlayers between the graphene sheets, silicon reacts with lithium and forms Li x Si alloys.4-6 Because the (de-)alloying reaction allows a higher lithium uptake per silicon atom (3579 mAh g −1Si , Li 15 Si 4 ) compared to the intercalation of lithium into the graphite host structure (372 mAh g −1 C , LiC 6 ), silicon offers an about ∼10 times larger theoretical specific capacity. However, while the intercalation chemistry reveals excellent cycling stability with only minor irreversible changes of the graphite's morphology (ca. +10%), 8 the (de-)alloying reaction causes significant morphological and chemical changes to the silicon particles, including (i) a large volume expansion of up to +280% and (ii) repeated breakage and formation of Si-Si bonds, which leads to severe mechanical stress and particle fracturing. [9][10][11][12] Upon continued cycling, these morphological changes cause a rapid capacity decay of silicon-based electrodes, which is largely driven by the electrical isolation of the fractured silicon particles.13-17 Nanometer-sized structures, including nanoparticles and nanowires, were shown to mitigate the mechanical stress which results from volumetric changes during the (de-)alloying reaction.12,18-20 However, there exists a trade-off, because the reduction of the particle size als...

We demonstrate a temperature sensor based on surface plasmon resonances supported by photonic crystal fibers (PCFs). Within the PCF, to enhance the sensitivity of the sensor, the air holes of the second layer are filled with a large thermo-optic coefficient liquid and some of those air holes are selectively coated with metal. Temperature variations will induce changes of coupling efficiencies between the fundamental core mode and the plasmonic mode, thus leading to different loss spectra that will be recorded. In this paper, variations of the dielectric constants of all components, including the metal, the filled liquid, and the fused silica, are considered. We conduct numerical calculations to analyze the mode profile and evaluate the power loss, demonstrating a temperature sensitivity as high as 720 pm/°C.

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Increasing demand for transport fuels has driven China to attach great importance to biodiesel development. To evaluate the environmental impacts caused by producing and driving with biodiesel made from soybean, jatropha, and microalgae under China conditions, the LCA methodology is used and the assessment results are compared with fossil diesel. The solar energy and CO 2 uptake in biomass agriculture and reduction of dependency on fossil fuels lead to a better performance on abiotic depletion potential (ADP), global warming potential (GWP), and ozone depletion potential (ODP) in the life cycle of biodiesel compared to fossil diesel. Except for ADP, GWP and ODP, producing and driving with biodiesel does not offer benefits in the other environmental impact categories including eutrophication, acidification, photochemical oxidation, and toxicity. Jatropha and microalgae are more competitive biodiesel feedstock compared to soybean in terms of all impacts. By using global normalization references and weighting method based on ecotaxes, the LCA single score for the assessed 10 mid-point impact categories of soybean, jatropha, and microalgae based biodiesel is 54, 37.2 and 3.67 times of that of fossil diesel, respectively. Improvement of biomass agriculture management, development of biodiesel production technologies, bettering energy structure and promoting energy efficiency in China are the key measures to lower environmental impacts in the life cycle of biodiesel in the future. Various sensitivity analyses have also been applied, which show that, choice of allocation method, transport distance, uncertainty in jatropha and microalgae yield and oil content, and recycling rate of harvest water of microalgae have significant influence on the life cycle environmental performance of biodiesel.