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.

As an n-type wide-bandgap (E g = 3.6 eV) semiconductor, SnO 2 is one of the most intensively studied materials owing to its myriad technologically important applications such as gas sensors and lithium rechargeable batteries. [1][2][3][4][5][6][7][8] To date, various nanostructures of SnO 2 , such as nanoparticles, [2] nanorods/belts/arrays, [3] nanotubes, [4] nanodisks, [5] nanoboxes, [6] hollow spheres, [7] and mesoporous structures, [8] have been prepared.Recently, hollow inorganic micro-and nanostructures have attracted considerable attention because of their promising applications such as nanoscale chemical reactors, efficient catalysts, drug-delivery carriers, and photonic building blocks. [9][10][11][12][13][14][15][16][17][18][19][20] Until now the general approach for preparation of hollow COMMUNICATIONS

Rechargeable lithium, sodium, and aluminum metal--based batteries are among the most versatile platforms for high--energy, cost--effective electrochemical energy storage. Non--uniform metal deposition and dendrite formation on the negative electrode during repeated cycles of charge and discharge are major hurdles to commercialization of energy storage devices based on each of these chemistries. A long held view is that unstable electrodeposition is a consequence of inherent characteristics of these metals and their inability to form uniform electrodeposits on surfaces with inevitable defects. We report on electrodeposition of lithium in simple liquid electrolytes and in nanoporous solids infused with liquid electrolytes. We find that simple liquid electrolytes reinforced with halogenated salt blends exhibit stable long--term cycling at room temperature, often with no signs of deposition instabilities over hundreds of cycles of charge and discharge and thousands of operating hours. We rationalize these observations with the help of surface energy data for the electrolyte/lithium interface and impedance analysis of the interface during different stages of cell operation. Our findings provide support for an important recent theoretical prediction that the surface mobility of lithium is significantly enhanced in the presence of lithium halide salts.High energy and safe electrochemical storage are critical components in multiple emerging fields of technology where portability is a requirement for performance and large--scale deployment. From advanced robotics, autonomous aircraft, to hybrid electric vehicles, the number of technologies demanding advanced electrochemical storage solutions is rising. The rechargeable lithium ion battery (LIB) has received considerable attention because of its high operating voltages, low internal resistance and minimal memory effects 1--7 . Unfortunately LIBs are currently operating close to their theoretical performance limits due to the relatively low capacity of the anode LiC 6 and the lithiated cathode materials (LiCoO 2 and LiFePO 4 ) in widespread use. It has long been understood that a rechargeable lithium metal battery (LMB), which eschewed the use of a carbon host at the anode can lead to as much as a ten--fold improvement in anode storage capacity (from 360 mAh g --1 to 3860 mAh g --1 ) and would open up opportunities for high energy un--lithiated cathode materials such as sulfur and oxygen, among others 8--10 . Together, these advances would lead to rechargeable batteries with step--change improvements in storage capacity relative to today's state of the art LIBs.A grand challenge in the field concerns the development of electrolytes, electrode, and battery systems configurations that prevent uneven electrodeposition of lithium and other metal anodes, and thereby eliminate dendrites at the nucleation step. 1 It is understood that without significant breakthroughs in this area, the promise of LMBs, as well as of storage platforms based on more earth abundant meta...

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Slowing down the shuttle: C@S nanocomposites (see TEM images) based on mesoporous, hollow carbon capsules were generated by a template‐based approach. As the cathode material in a Li–S secondary battery, they display outstanding electrochemical features attributed to sequestration of elemental sulfur in the carbon capsules and to its favorable effect in limiting polysulfide shuttling as well as to enhanced electron transport from the sulfur.

The propensity of metals to form irregular and nonplanar electrodeposits at liquid-solid interfaces has emerged as a fundamental barrier to high-energy, rechargeable batteries that use metal anodes. We report an epitaxial mechanism to regulate nucleation, growth, and reversibility of metal anodes. The crystallographic, surface texturing, and electrochemical criteria for reversible epitaxial electrodeposition of metals are defined and their effectiveness demonstrated by using zinc (Zn), a safe, low-cost, and energy-dense battery anode material. Graphene, with a low lattice mismatch for Zn, is shown to be effective in driving deposition of Zn with a locked crystallographic orientation relation. The resultant epitaxial Zn anodes achieve exceptional reversibility over thousands of cycles at moderate and high rates. Reversible electrochemical epitaxy of metals provides a general pathway toward energy-dense batteries with high reversibility.

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Synthesis of nanocrystals with exposed high-energy facets is a well-known challenge in many fields of science and technology. The higher reactivity of these facets simultaneously makes them desirable catalysts for sluggish chemical reactions and leads to their small populations in an equilibrated crystal. Using anatase TiO 2 as an example, we demonstrate a facile approach for creating high surface area, stable nanosheets comprised of nearly 100% exposed (001) facets. Our approach relies on spontaneous assembly of the nanosheets into three-dimensional, hierarchical spheres that stabilizes them from collapse. We show that the high surface density of exposed TiO 2 (001) facets leads to fast lithium insertion/deinsertion processes in batteries that mimic features seen in high power electrochemical capacitors.2