High-performance lithium battery anodes using silicon nanowires.
ABSTRACT There is great interest in developing rechargeable lithium batteries with higher energy capacity and longer cycle life for applications in portable electronic devices, electric vehicles and implantable medical devices. Silicon is an attractive anode material for lithium batteries because it has a low discharge potential and the highest known theoretical charge capacity (4,200 mAh g(-1); ref. 2). Although this is more than ten times higher than existing graphite anodes and much larger than various nitride and oxide materials, silicon anodes have limited applications because silicon's volume changes by 400% upon insertion and extraction of lithium which results in pulverization and capacity fading. Here, we show that silicon nanowire battery electrodes circumvent these issues as they can accommodate large strain without pulverization, provide good electronic contact and conduction, and display short lithium insertion distances. We achieved the theoretical charge capacity for silicon anodes and maintained a discharge capacity close to 75% of this maximum, with little fading during cycling.
SourceAvailable from: Anna Fontcuberta i Morral[Show abstract] [Hide abstract]
ABSTRACT: The ability to rationally tune the morphology of nanostructures is a fundamental milestone in nanoscale engineering. In particular, the possibility to switch between different shapes within the same material system represents a further step in the development of complex nanoscale devices and it increases the potential of nanostructures in practical applications. We recently reported a new form of InAs nanostructures growing epitaxially on Si substrates as vertical V-shaped membranes. Here we demonstrate the possibility of modifying the shape of these nanomembranes and turning them into nanowires by modulating the surface roughness of the substrate by varying the surface treatment. We show that the growth of nanomembranes is favored on smooth surfaces. Conversely rough surfaces enhance the growth of nanowires. We also show that the V/III ratio plays a key role in determining the absolute yield, i.e. how many nanostructures form during growth. These results envisage a new degree of freedom in the engineering of bottom-up nanostructures and contribute to the achievement of nanostructure networks.Journal of Crystal Growth 06/2015; 420. DOI:10.1016/j.jcrysgro.2015.01.040 · 1.69 Impact Factor
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ABSTRACT: Silicon is considered as a promising anode material for lithium ion batteries. Despite the great attention on Si anode materials, a consistent description of the diffusion and reaction mechanism at the reaction front of crystalline silicon, amorphous silicon, and delithiated amorphous silicon has not yet been proposed. To better understand those mechanisms, a new reaction-controlled diffusion formulation is proposed. The new formulation makes use of the bond-breaking energy barrier E 0 as the key physical quantity. With the consideration of different values of E 0 , the two-phase diffusion during initial lithiation of both crystalline Si and amorphous Si can be well represented with an evident reaction front. In addition, by varying E 0 , the one phase lithiation of amorphous Si, obtained after the delithiation process, can be captured with the new formulation. The effect of deformation, hydrostatic pressure at the reaction front, and Li concentration level on the reaction front velocity is taken into account in the proposed model. Numerical simulations are provided to support the model.04/2015; DOI:10.1016/j.eml.2015.04.005
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ABSTRACT: Silicon has been critically examined for its potential use as an electrode material for Li-ion batteries. Diffusive transport of Li-ions in the crystalline silicon anode is one of the key mechanisms that controls the deformation during lithiation, the rate of the charge-discharge cycle, and eventual mechanical failure. The use of amorphous silicon, instead of its crystalline counterpart, is considered to offer several advantages. The atomistic mechanisms underpinning diffusive transport of Li-ions in amorphous silicon are, however, poorly understood. Conventional molecular dynamics, if used to obtain atomistic insights into the Li-ion transport mechanism, suffers from several disadvantages: the relaxation times of Li ion diffusion in many of the diffusion pathways in amorphous Si are well beyond the short time scales of conventional molecular dynamics. In this work we utilize a sequence of approaches that involve the employment of a novel and recently developed potential energy surface sampling method, kinetic Monte Carlo, and the transition state theory to obtain a realistic evaluation of Li-ion diffusion pathways in amorphous Si. Diffusive pathways are not a priori set but rather emerge naturally as part of our computation. We elucidate the comparative differences between Li-ion diffusion in amorphous and crystalline Si as well as compare our results with past studies based on other methods.Mechanics of Materials 04/2015; DOI:10.1016/j.mechmat.2015.04.001 · 2.23 Impact Factor