Graphene: a two-dimensional platform for lithium storage

Lithium ion batteries (LIBs) have attracted great attention due to their high energy density, low maintenance requirements, and relatively low self-discharge. Since the electrode materials hold the key for the electrochemical performance of LIBs, the design and synthesis of unconventional electrode materials with high lithium-storage capacities are the current focus in LIB research. In the last few years, a great deal of effort has been directed toward graphene as the electrode material for LIBs owing to its high intrinsic surface area, high electrical conductivity, and good compatibility with other electrochemically active components. This review paper outlines the componential and structural design for graphene-based hybrids in LIBs with enhanced electrochemical performance. The typical fabrication methods and structure-property relationships of these hybrids are discussed.

A proposed voltage dependence of the ionic strength of a confined electrolyte based on a grand canonical ensemble model

Electrodes with highly porous morphologies are of great technological interest, as their exceptionally high specific surface areas make them ideal for use in capacitors, battery electrodes and electrochemical sensors. There is a large body of research focusing on the structure of confined electrolytes in these systems, but the majority of these studies focus on cases where the length scale of the porous domain is equal to or less than the Debye screening length of the electrolyte. In this work, we use a thermodynamic model to consider the structure of electrolytes in mesoscale domains, where the pore dimensions are significantly larger than the Debye screening length. In this limit, the interface is screened by the electrochemical double layer and the enclosed volume primarily consists of an electroneutral 'bulk liquid' domain. Despite the absence of direct interactions between ions in the bulk domain and the charged interface, we show that minimization of the free energy of the system leads to a reduction in the ionic strength of the electrolyte within the bulk liquid domain of the pore. Based on our model studies, we anticipate that this depletion will apply for porous domains with widths of the order of 50-200 nm even under mild experimental conditions and low applied voltages. The results imply relationships between electrolyte strength, surface morphology and applied voltage that may be important in device design.

Synthesis of one-dimensional hierarchical NiO hollow nanostructures with enhanced supercapacitive performance

One-dimensional hierarchical hollow nanostructures composed of NiO nanosheets are successfully synthesized through a facile carbon nanofiber directed solution method followed by a simple thermal annealing treatment. With the advantages of high electro-active surface area, carbon nanofiber supported robust structure and short ion and electron transport pathways, the hierarchical hybrid nanostructures deliver largely enhanced capacitance with excellent cycling stability when evaluated as electrode materials for supercapacitors. More specifically, a high capacitance of 642 F g(-1) is achieved when the charge-discharge current density is 3 A g(-1) and the total capacitance loss is only 5.6% after 1000 cycles.

Subnanometer Thin β-Indium Sulfide Nanosheets

Nanosheets are a peculiar kind of nanomaterials that are grown two-dimensionally over a micrometer in length and a few nanometers in thickness. Wide varieties of inorganic semiconductor nanosheets are already reported, but controlling the crystal growth and tuning their thickness within few atomic layers have not been yet explored. We investigate here the parameters that determine the thickness and the formation mechanism of subnanometer thin (two atomic layers) cubic indium sulfide (In2S3) nanosheets. Using appropriate reaction condition, the growth kinetics is monitored by controlling the decomposition rate of the single source precursor of In2S3 as a function of nucleation temperature. The variation in the thickness of the nanosheets along the polar [111] direction has been correlated with the rate of evolved H2S gas, which in turn depends on the rate of the precursor decomposition. In addition, it has been observed that the thickness of the In2S3 nanosheets is related to the nucleation temperature.

Mesoporous NiO crystals with dominantly exposed {110} reactive facets for ultrafast lithium storage

Faceted crystals with exposed highly reactive planes have attracted intensive investigations for applications such as hydrogen production, enhanced catalytic activity, and electrochemical energy storage and conversion. Herein, we report the synthesis of mesoporous NiO crystals with dominantly exposed {110} reactive facets by the thermal conversion of hexagonal Ni(OH)₂ nanoplatelets. When applied as anode materials in lithium-ion batteries, mesoporous NiO crystals exhibit a high reversible lithium storage capacity of 700 mAh g⁻¹ at 1 C rate in 100 cycles and an excellent cyclability. In particular, the dominantly exposed {110} reactive facets and mesoporous nanostructure of NiO crystals lead to ultrafast lithium storage, which mimics the high power delivery of supercapacitors.

Layer-by-layer self-assembly in the development of electrochemical energy conversion and storage devices from fuel cells to supercapacitors

As one of the most effective synthesis tools, layer-by-layer (LbL) self-assembly technology can provide a strong non-covalent integration and accurate assembly between homo- or hetero-phase compounds or oppositely charged polyelectrolytes, resulting in highly-ordered nanoscale structures or patterns with excellent functionalities and activities. It has been widely used in the developments of novel materials and nanostructures or patterns from nanotechnologies to medical fields. However, the application of LbL self-assembly in the development of highly efficient electrocatalysts, specific functionalized membranes for proton exchange membrane fuel cells (PEMFCs) and electrode materials for supercapacitors is a relatively new phenomenon. In this review, the application of LbL self-assembly in the development and synthesis of key materials of PEMFCs including polyelectrolyte multilayered proton-exchange membranes, methanol-blocking Nafion membranes, highly uniform and efficient Pt-based electrocatalysts, self-assembled polyelectrolyte functionalized carbon nanotubes (CNTs) and graphenes will be reviewed. The application of LbL self-assembly for the development of multilayer nanostructured materials for use in electrochemical supercapacitors will also be reviewed and discussed (250 references).

Layer-by-layer assembled MoO₂-graphene thin film as a high-capacity and binder-free anode for lithium-ion batteries

Thin films of MoO(2) nanoparticles and graphene sheets are created by layer-by-layer (LBL) assembly as binder-free anodes for lithium-ion batteries. Both anionic polyoxometalate clusters and graphene oxide nanosheets with oxygen functional groups on both basal planes and edges are assembled into LBL films with the aid of a cationic polyelectrolyte. After a subsequent thermal treatment in an Ar-H(2) atmosphere, hybrid MoO(2)-graphene films with three-dimensionally interconnected nanopores are formed, which comprise ultrafine MoO(2) nanoparticles homogeneously embedded in the porous network of graphene nanosheets. When used as an anode for lithium-ion batteries, the MoO(2)-graphene thin-film electrode shows superior electrochemical performance with high specific capacity and excellent cyclability. A high specific capacity of 675.9 mA h g(-1) after 100 discharge-charge cycles is achieved, indicating a promising anode candidate for lithium-storage applications.