Sol-Gel Electrophoretic Deposition Process Improves Dye-Sensitized Solar Cells
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Nanostructured Lithium Sulfide/Silicon Electrode Design Quadruples Theoretical Specific Energy of Rechargeable Batteries With recent advances in high-capacity anodes, the limiting factor in producing rechargeable batteries with a high specific energy (for use in electric vehicles and portable electronics) now stems from the relatively low specific capacity of the corresponding cathodes. While sulfur-based cathodes in combination with lithium anodes have the potential to overcome these capacity limitations, the use of elemental Li as the anode leads to serious safety concerns—Li dendrites form during cycling and can penetrate the thin polymer layer separating the two electrodes, leading to short circuits and potential explosions. Y. Yang, A.T. McDowell, A. Jackson, and colleagues at Stanford University, however, combat these issues by pairing sulfur’s lithiated counterpart (Li2S) in the cathode with a high capacity, low potential silicon nanowire anode to create a novel nanostructured rechargeable battery with a theoretical specific energy four times that of existing LiCoO2/graphite or LiFePO4/ graphite systems. As described in the April 14 issue of Nano Letters (DOI: 10.1021/nl100504q; p. 1486), on the cathode side of the battery depicted in Figure 1, the researchers first diffuse sulfur into the sub-5 nm pores of ordered mesoporous carbon and then convert it into Li2S by a reaction with n-butyllithium. The ordered mesoporous carbon consists of hexagonally arranged 7–8-nm thick nanorods around 3–4 nm pores. The interconnected carbon rods act as conductive pathways, providing electronic access to the insulating Li2S trapped within the pores while the submicrometer
Sol-Gel Electrophoretic Deposition Process Improves Dye-Sensitized Solar Cells Dye-sensitized solar cells (DSSCs) hold significant promise as a lower cost alternative to conventional silicon photovoltaics. Their ability to be fabricated using inexpensive techniques on flexible plastic substrates has attracted considerable research interest since they were first demonstrated almost 20 years ago. However, their efficiencies are limited by electron losses in the anode. Now A. Zaban, L. Grinis, and their colleagues at Bar-Ilan University in Ramat Gan, Israel have demonstrated a new low-temperature coating technique using sol-gel processing and electro -
Anode Silicon Nanowires
Cathode Mesoporous Carbon/Li2S Nanocomposite
size of the carbon particles shortens Li diffusion paths—this design overcomes the slow kinetics (and poor electronic conductivity) inherent to Li2S-based cathodes. On
the anode side, silicon nanowires are grown by the vapor-liquid-solid (VLS) method onto a stainless steel substrate. Silicon is known to have a very high theoretical capacity (4212 mAh/g) and low potential (~0.3 V versus Li/Li+), and unlike previous Si-based electrodes, the nanowire architecture allows for the requisite 400% volume change associated with the insertion and extraction of Li without disintegration or significant capacity fading. The resulting higher capacity a
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