Beyond intercalation-based Li-ion batteries: the state of the art and challenges of electrode materials reacting through conversion reactions

Nanostructured metal oxide-based materials as advanced anodes for lithium-ion batteries

The search for new electrode materials for lithium-ion batteries (LIBs) has been an important way to satisfy the ever-growing demands for better performance with higher energy/power densities, improved safety and longer cycle life. Nanostructured metal oxides exhibit good electrochemical properties, and they are regarded as promising anode materials for high-performance LIBs. In this feature article, we will focus on three different categories of metal oxides with distinct lithium storage mechanisms: tin dioxide (SnO(2)), which utilizes alloying/dealloying processes to reversibly store/release lithium ions during charge/discharge; titanium dioxide (TiO(2)), where lithium ions are inserted/deinserted into/out of the TiO(2) crystal framework; and transition metal oxides including iron oxide and cobalt oxide, which react with lithium ions via an unusual conversion reaction. For all three systems, we will emphasize that creating nanomaterials with unique structures could effectively improve the lithium storage properties of these metal oxides. We will also highlight that the lithium storage capability can be further enhanced through designing advanced nanocomposite materials containing metal oxides and other carbonaceous supports. By providing such a rather systematic survey, we aim to stress the importance of proper nanostructuring and advanced compositing that would result in improved physicochemical properties of metal oxides, thus making them promising negative electrodes for next-generation LIBs.

Structural and mechanistic revelations on an iron conversion reaction from pair distribution function analysis

Not simply small particles: pair distribution function analysis yields comprehensive insights into the electrochemical reaction of α-Fe(2)O(3) with lithium. The metallic Fe formed in this reaction was found to be defect-rich nanoparticles that restructure continuously without growing-an unusual characteristic likely linked to its highly reversible capacity.

Fe3O4/Fe/carbon composite and its application as anode material for lithium-ion batteries

A plum pudding-like Fe(3)O(4)/Fe/carbon composite was synthesized by a sol-gel polymerization followed by a heat-treatment process and characterized by X-ray diffraction, Raman spectroscopic analysis, thermogravimetric analysis, scanning electron microscopy with energy-dispersive spectroscopy, transmission electron microscopy, and electrochemical test. In this composite, uniform spherical Fe(3)O(4)/Fe nanoparticles of about 100 nm were embedded into carbon matrix with high monodispersion. As-prepared Fe(3)O(4)/Fe/carbon composite electrode exhibits a stable and reversible capacity of over 600 mA h g(-1) at a current of 50 mA g(-1) between 0.002 V and 3.0 V, as well as excellent rate capability. The plum pudding-like structure, in which trace Fe promotes conductivity and carbon matrix mediates the volume change, can enhance the cycling performance and rate capability of Fe(3)O(4) electrode. This unique structure is valuable for the preparation of other electrode materials.

Selective crystallization with preferred lithium-ion storage capability of inorganic materials

Lithium-ion batteries are supposed to be a key method to make a more efficient use of energy. In the past decade, nanostructured electrode materials have been extensively studied and have presented the opportunity to achieve superior performance for the next-generation batteries which require higher energy and power densities and longer cycle life. In this article, we reviewed recent research activities on selective crystallization of inorganic materials into nanostructured electrodes for lithium-ion batteries and discuss how selective crystallization can improve the electrode performance of materials; for example, selective exposure of surfaces normal to the ionic diffusion paths can greatly enhance the ion conductivity of insertion-type materials; crystallization of alloying-type materials into nanowire arrays has proven to be a good solution to the electrode pulverization problem; and constructing conversion-type materials into hollow structures is an effective approach to buffer the volume variation during cycling. The major goal of this review is to demonstrate the importance of crystallization in energy storage applications.

Size-tunable, hexagonal plate-like Cu3P and Janus-like Cu-Cu3P nanocrystals

We describe two synthesis approaches to colloidal Cu(3)P nanocrystals using trioctylphosphine (TOP) as phosphorus precursor. One approach is based on the homogeneous nucleation of small Cu(3)P nanocrystals with hexagonal plate-like morphology and with sizes that can be tuned from 5 to 50 nm depending on the reaction time. In the other approach, metallic Cu nanocrystals are nucleated first and then they are progressively phosphorized to Cu(3)P. In this case, intermediate Janus-like dimeric nanoparticles can be isolated, which are made of two domains of different materials, Cu and Cu(3)P, sharing a flat epitaxial interface. The Janus-like nanoparticles can be transformed back to single-crystalline copper particles if they are annealed at high temperature under high vacuum conditions, which makes them an interesting source of phosphorus. The features of the Cu-Cu(3)P Janus-like nanoparticles are compared with those of the striped microstructure discovered more than two decades ago in the rapidly quenched Cu-Cu(3)P eutectic of the Cu-P alloy, suggesting that other alloy/eutectic systems that display similar behavior might give origin to nanostructures with flat, epitaxial interface between domains of two diverse materials. Finally, the electrochemical properties of the copper phosphide plates are studied, and they are found to be capable of undergoing lithiation/delithiation through a displacement reaction, while the Janus-like Cu-Cu(3)P particles do not display an electrochemical behavior that would make them suitable for applications in batteries.

Electrodeposition of Lithium/Polystyrene Composite Electrodes from an Ionic Liquid: First Attempts

One challenge in the use of metallic lithium in secondary lithium ion or lithium air batteries is the dendritic growth of lithium upon repeated cycling which might either lead to a short circuit or at least to an uneven current distribution and bad cycling stability. In the present paper we present our first results on the electrodeposition of lithium from an ionic liquid within the voids of a polystyrene opal structure on copper. For this purpose polystyrene spheres with an average diameter of about 600 nm were applied onto a copper sheet by a simple dipping process resulting in a layer thickness of about 10 μm. Lithium can be deposited within this polymer structure without damaging it and the subsequent dissolution of the polystyrene spheres delivers a macroporous lithium film, proving that a mechanically stable composite electrode is feasible.

Eruption combustion synthesis of NiO/Ni nanocomposites with enhanced properties for dye-absorption and lithium storage

Large-scale energy-efficient productions of oxide nanoparticles are of great importance in energy and environmental applications. In nature, volcano eruptions create large amounts of volcano ashes within a short duration. Inspired by such phenomena, we report herein our first attempt to achieve an artificial volcano for mass productions of various oxide nanoparticles with enhanced properties for energy and environmental applications. The introduction of NaF into the solution combustion synthesis (SCS), which is a generally adopted synthetic route for mass productions of various oxide nanoparticles, results in better particle dispersity and a drastic increase in specific surface area compared to the conventional SCS. In a fixed dosage of NaF, a new eruption combustion pattern emerges, which may be contributed to the more gas evolution, lower apparent density, and weaker interparticle force. The novel eruption combustion pattern observed in SCS provides a versatile alternative for SCS to control combustion behavior, microstructure, and property of the products. NiO/Ni nanocomposite yielded by the new approach shows an ideal dye-absorption ability as well as lithium storage capacity. The new SCS pattern reported in this paper is versatile, emerging in various systems of Ni-Co-O, Co-O, La-O, Ni-Co-O, Zn-Co-O, and La-Ni-O.

Self-assembled hierarchical MoO2/graphene nanoarchitectures and their application as a high-performance anode material for lithium-ion batteries

Self-assembled hierarchical MoO(2)/graphene nanoarchitectures have been fabricated on a large scale through a facile solution-phase process and subsequent reduction of the Mo-precursor/graphene composite. The as-formed MoO(2)/graphene nanohybrid as an anode material for lithium-ion batteries exhibits not only a highly reversible capacity but also an excellent cycling performance as well as good rate capability. Results show that the hierarchical rods made of primary MoO(2) nanocrystals are uniformly encapsulated within the graphene sheets. The synergistic effect of the hierarchical nanoarchitecture and the conducting graphene support may contribute to the enhanced electrochemical performances of the hybrid MoO(2)/graphene electrode. This work presents a facile synthetic strategy that is potentially competitive for scaling-up industrial production. Besides, the MoO(2)/graphene hybrids with a well-defined hierarchical topology not only provide flexible building blocks for advanced functional devices, but are also ideal candidates for studying their nanoarchitecture-dependent performances in catalytic and electronic applications.

Three-dimensional imaging of chemical phase transformations at the nanoscale with full-field transmission X-ray microscopy

The ability to probe morphology and phase distribution in complex systems at multiple length scales unravels the interplay of nano- and micrometer-scale factors at the origin of macroscopic behavior. While different electron- and X-ray-based imaging techniques can be combined with spectroscopy at high resolutions, owing to experimental time limitations the resulting fields of view are too small to be representative of a composite sample. Here a new X-ray imaging set-up is proposed, combining full-field transmission X-ray microscopy (TXM) with X-ray absorption near-edge structure (XANES) spectroscopy to follow two-dimensional and three-dimensional morphological and chemical changes in large volumes at high resolution (tens of nanometers). TXM XANES imaging offers chemical speciation at the nanoscale in thick samples (>20 µm) with minimal preparation requirements. Further, its high throughput allows the analysis of large areas (up to millimeters) in minutes to a few hours. Proof of concept is provided using battery electrodes, although its versatility will lead to impact in a number of diverse research fields.

NiO nanosheets grown on graphene nanosheets as superior anode materials for Li-ion batteries

This paper reports a hydrothermal preparation of NiO-graphene sheet-on-sheet and nanoparticle-on-sheet nanostructures. The sheet-on-sheet nanocomposite showed highly reversible large capacities at a common current of 0.1 C and good rate capabilities. A large initial charge capacity of 1056 mAh/g was observed for the sheet-on-sheet composite at 0.1 C, which decreased by only 2.4% to 1031 mAh/g after 40 cycles of discharge and charge. This cycling performance is better than that of NiO nanosheets, graphene nanosheets, NiO-graphene nanoparticle-on-sheet, and previous carbon/carbon nanotube supported NiO composites. It is believed that the mechanical stability and electrical conductivity of NiO nanosheets are increased by graphene nanosheets (GNS), the aggregation or restacking of which to graphite platelets are, on the other hand, effectively prevented by NiO nanosheets.