[Liu, Chang; Li, Feng; Ma, Lai-Peng; Cheng, Hui-Ming] Chinese Acad Sci, Inst Met Res, Shenyang Natl Lab Mat Sci, Shenyang 110016, Peoples R China.;Cheng, HM (reprint author), Chinese Acad Sci, Inst Met Res, Shenyang Natl Lab Mat Sci, 72 Wenhua Rd, Shenyang 110016, Peoples R China;cheng@imr.ac.cn

Advanced Materials for Energy Storage

Rechargeable lithium-sulfur batteries.

Hollow micro-/nanostructures are of great interest in many current and emerging areas of technology. Perhaps the best-known example of the former is the use of fly-ash hollow particles generated from coal power plants as partial replacement for Portland cement, to produce concrete with enhanced strength and durability. This review is devoted to the progress made in the last decade in synthesis and applications of hollow micro-/nanostructures. We present a comprehensive overview of synthetic strategies for hollow structures. These strategies are broadly categorized into four themes, which include well-established approaches, such as conventional hard-templating and soft-templating methods, as well as newly emerging methods based on sacrificial templating and template-free synthesis. Success in each has inspired multiple variations that continue to drive the rapid evolution of the field. The Review therefore focuses on the fundamentals of each process, pointing out advantages and disadvantages where appropriate. Strategies for generating more complex hollow structures, such as rattle-type and nonspherical hollow structures, are also discussed. Applications of hollow structures in lithium batteries, catalysis and sensing, and biomedical applications are reviewed.

Hollow Micro-/Nanostructures: Synthesis and Applications**

Metal Oxides and Oxysalts as Anode Materials for Li Ion Batteries

Coinage metals, such as Au, Ag, and Cu, have been important materials throughout history.1 While in ancient cultures they were admired primarily for their ability to reflect light, their applications have become far more sophisticated with our increased understanding and control of the atomic world. Today, these metals are widely used in electronics, catalysis, and as structural materials, but when they are fashioned into structures with nanometer-sized dimensions, they also become enablers for a completely different set of applications that involve light. These new applications go far beyond merely reflecting light, and have renewed our interest in maneuvering the interactions between metals and light in a field known as plasmonics.2–6

In plasmonics, the metal nanostructures can serve as antennas to convert light into localized electric fields (E-fields) or as waveguides to route light to desired locations with nanometer precision. These applications are made possible through a strong interaction between incident light and free electrons in the nanostructures. With a tight control over the nanostructures in terms of size and shape, light can be effectively manipulated and controlled with unprecedented accuracy.3,7 While many new technologies stand to be realized from plasmonics, with notable examples including superlenses,8 invisible cloaks,9 and quantum computing,10,11 conventional technologies like microprocessors and photovoltaic devices could also be made significantly faster and more efficient with the integration of plasmonic nanostructures.12–15 Of the metals, Ag has probably played the most important role in the development of plasmonics, and its unique properties make it well-suited for most of the next-generation plasmonic technologies.16–18

1.1. What is Plasmonics?
Plasmonics is related to the localization, guiding, and manipulation of electromagnetic waves beyond the diffraction limit and down to the nanometer length scale.4,6 The key component of plasmonics is a metal, because it supports surface plasmon polariton modes (indicated as surface plasmons or SPs throughout this review), which are electromagnetic waves coupled to the collective oscillations of free electrons in the metal.

While there are a rich variety of plasmonic metal nanostructures, they can be differentiated based on the plasmonic modes they support: localized surface plasmons (LSPs) or propagating surface plasmons (PSPs).5,19 In LSPs, the time-varying electric field associated with the light (Eo) exerts a force on the gas of negatively charged electrons in the conduction band of the metal and drives them to oscillate collectively. At a certain excitation frequency (w), this oscillation will be in resonance with the incident light, resulting in a strong oscillation of the surface electrons, commonly known as a localized surface plasmon resonance (LSPR) mode.20 This phenomenon is illustrated in Figure 1A. Structures that support LSPRs experience a uniform Eo when excited by light as their dimensions are much smaller than the wavelength of the light.



Figure 1

Schematic illustration of the two types of plasmonic nanostructures discussed in this article as excited by the electric field (Eo) of incident light with wavevector (k). In (A) the nanostructure is smaller than the wavelength of light and the free electrons ...



In contrast, PSPs are supported by structures that have at least one dimension that approaches the excitation wavelength, as shown in Figure 1B.4 In this case, the Eo is not uniform across the structure and other effects must be considered. In such a structure, like a nanowire for example, SPs propagate back and forth between the ends of the structure. This can be described as a Fabry-Perot resonator with resonance condition l=nλsp, where l is the length of the nanowire, n is an integer, and λsp is the wavelength of the PSP mode.21,22 Reflection from the ends of the structure must also be considered, which can change the phase and resonant length. Propagation lengths can be in the tens of micrometers (for nanowires) and the PSP waves can be manipulated by controlling the geometrical parameters of the structure.23

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Controlling the synthesis and assembly of silver nanostructures for plasmonic applications

Lithium sulfide is a promising cathode material for high-energy lithium ion batteries because, unlike elemental sulfur, it obviates the need for metallic lithium anodes. Like elemental sulfur, however, a successful lithium sulfide cathode requires an inherent mechanism for preventing lithium polysulfide dissolution and shuttling during electrochemical cycling. A new scheme is proposed to create composites based on lithium sulfide uniformly dispersed in a carbon host, which serve to sequester polysulfides. The synthesis methodology makes use of interactions between lithium ions in solution and nitrile groups uniformly distributed along the chain backbone of a polymer precursor (e.g., polyacrylonitrile), to control the distribution of lithium sulfide in the host material. The Li2S–carbon composites obtained by carbonizing the precursor are evaluated as cathode materials in a half-cell lithium battery, and are shown to yield high galvanic charge/discharge capacities and excellent Coulombic efficiency, demons...

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Lithium–Sulfur Battery Cathode Enabled by Lithium–Nitrile Interaction

This article is part of an ongoing series celebrating the 25th anniversary of Advanced Materials. This publication is based on work supported in part by the National Science Foundation, Award No. DMR-1006323; by the Energy Materials Center at Cornell, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences under Award Number DE-SC0001086; and by Award No. KUS-C1-018-02, made by King Abdullah University of Science and Technology (KAUST). This work made use of the electron microscopy facility at the Cornell Center for Materials Research (CCMR), an NSF-supported MRSEC through Grant DMR-1120296.

25th Anniversary Article: Polymer–Particle Composites: Phase Stability and Applications in Electrochemical Energy Storage

Lithium–sulfur batteries are among the most promising candidates for next-generation rechargeable lithium batteries in view of recent progress on sulfur–carbon composite cathodes. However, further progress on such batteries is hampered by their concomitant need for a metallic lithium anode, which introduces new challenges associated with uneven electrodeposition and lithium dendrite formation. Here we report a method of creating lithium sulfide–carbon composites as cathode materials, which can be paired with high-capacity anodes other than metallic lithium. Lithium sulfide is dispersed in a porous carbon matrix, which serves to improve its electrical conductivity and provides a framework for sequestration of sulfur and lithium polysulfides. The in situ synthesis approach allows facile, scalable synthesis of lithium sulfide–carbon composite materials that exhibit improved electrochemical properties. We also investigate the effect of lithium polysulfides dissolved in the electrolyte on the stability and cycling behavior of Li2S–carbon composite cathodes.

In situ synthesis of lithium sulfide–carbon composites as cathode materials for rechargeable lithium batteries

Transition metal oxides are actively investigated as anode materials for lithium-ion batteries (LIBs), and their nanocomposites with carbon frequently show better performance in galvanostatic cycling studies, compared to the pristine metal oxide. An in situ, scalable method for creating a variety of transition metal oxide–carbon nanocomposites has been developed based on free-radical polymerization and cross-linking of poly(acrylonitrile) in the presence of the metal oxide precursor containing vinyl groups. The approach yields a cross-linked polymer network, which uniformly incorporates nanometre-sized transition metal oxide particles. Thermal treatment of the organic–inorganic hybrid material produces nearly monodisperse metal oxide nanoparticles uniformly embedded in a porous carbon matrix. Cyclic voltammetry and galvanostatic cycling electrochemical measurements in a lithium half-cell are used to evaluate the electrochemical properties of a Fe3O4–carbon composite created using this approach. These measurements reveal that when used as the anode in a lithium battery, the material exhibits stable cycling performance at both low and high current densities. We further show that the polymer/nanoparticle copolymerization approach can be readily adapted to synthesize metal oxide/carbon nanocomposites based on different particle chemistries for applications in both the anode and cathode of LIBs.

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Zichao Yang

Papers

Hollow Micro-/Nanostructures: Synthesis and Applications**

Lithium–Sulfur Battery Cathode Enabled by Lithium–Nitrile Interaction

25th Anniversary Article: Polymer–Particle Composites: Phase Stability and Applications in Electrochemical Energy Storage

In situ synthesis of lithium sulfide–carbon composites as cathode materials for rechargeable lithium batteries

An in situ method of creating metal oxide–carbon composites and their application as anode materials for lithium-ion batteries