Fang

Pseudocapacitance-tuned high-rate and long-term cyclability of NiCo2S4 hexagonal nanosheets prepared by vapor transformation for lithium storage

The high conductivity of bimetallic thiospinel NiCo2S4 endows energy storage devices with very fascinating performance. However, the unsatisfactory rate capability and long-term cyclability of this material series significantly limit their large-scale practical applications such as in electric vehicles and hybrid electric vehicles. Herein, we successfully synthesized NiCo2S4 hexagonal nanosheets with a large lateral dimension of ∼1.35 μm and a thickness of ∼30 nm through a vapor transformation method. The dynamic transformation process of the NiCo2S4 polycrystalline nanosheets from NiCo-hydroxide has been revealed in detail. Originating from their two-dimensional thin-sheet structure with a high aspect ratio, the induced extrinsic capacitive contribution as high as 91% makes them an ideal candidate for high-capacity and high-rate lithium-ion anodes. The NiCo2S4 nanosheets deliver a reversible capacity of 607 mA h g−1 upon 800 cycles at a current density of 2 A g−1. This outstanding long cycle performance sheds light on the structural design of electrode materials for high-rate lithium-ion batteries.

Three-Dimensional Graphene/Single-Walled Carbon Nanotube Aerogel Anchored with SnO2 Nanoparticles for High Performance Lithium Storage

A unique 3D graphene-single walled carbon nanotube (G-SWNT) aerogel anchored with SnO2 nanoparticles (SnO2@G-SWCNT) is fabricated by the hydrothermal self-assembly process. The influences of mass ratio of SWCNT to graphene on structure and electrochemical properties of SnO2@G-SWCNT are investigated systematically. The SnO2@G-SWCNT composites show excellent electrochemical performance in Li-ion batteries; for instance, at a current density of 100 mA g-1, a specific capacity of 758 mAh g-1 was obtained for the SnO2@G-SWCNT with 50% SWCNT in G-SWCNT and the Coulombic efficiency is close to 100% after 200 cycles; even at current density of 1 A g-1, it can still maintain a stable specific capacity of 537 mAh g-1 after 300 cycles. It is believed that the 3D G-SWNT architecture provides a flexible conductive matrix for loading the SnO2, facilitating the electronic and ionic transportation and mitigating the volume variation of the SnO2 during lithiation/delithiation. This work also provides a facile and reasonable strategy to solve the pulverization and agglomeration problem of other transition metal oxides as electrode materials.

Bottom-up Approach Design, Band Structure, and Lithium Storage Properties of Atomically Thin γ-FeOOH Nanosheets

As a novel class of soft matter, two-dimensional (2D) atomic nanosheet-like crystals have attracted much attention for energy storage devices due to the fact that nearly all of the atoms can be exposed to the electrolyte and involved in redox reactions. Herein, atomically thin γ-FeOOH nanosheets with a thickness of ∼1.5 nm are synthesized in a high yield, and the band and electronic structures of the γ-FeOOH nanosheet are revealed using density-functional theory calculations for the first time. The rationally designed γ-FeOOH@rGO composites with a heterostacking structure are used as an anode material for lithium-ion batteries (LIBs). A high reversible capacity over 850 mAh g(-1) after 100 cycles at 200 mA g(-1) is obtained with excellent rate capability. The remarkable performance is attributed to the ultrathin nature of γ-FeOOH nanosheets and 2D heterostacking structure, which provide the minimized Li(+) diffusion length and buffer zone for volume change. Further investigation on the Li storage electrochemical mechanism of γ-FeOOH@rGO indicates that the charge-discharge processes include both conversion reaction and capacitive behavior. This synergistic effect of conversion reaction and capacitive behavior originating from 2D heterostacking structure casts new light on the development of high-energy anode materials.

Carbon nanomaterial-assisted morphological tuning for thermodynamic and kinetic destabilization in sodium alanates

In the present work, we develop an effective strategy, i.e., carbon nanomaterial-assisted morphological tuning, for both thermodynamic and kinetic destabilization in complex hydrides based on the interaction between the complex anion and the carbon matrix. The NaAlH4/carbon nanomaterials of graphene nanosheets (GNs), fullerene (C60) and mesoporous carbon (MC) were selected as model systems for illustrating the positive effect of carbon nanomaterial-assisted morphological tuning. It is demonstrated that through the dissolution–recrystallization process, the morphologies of NaAlH4 can be altered from the scale-like continuous structure for the GN-assisted sample, to flower-like structures with diameters ranging from 5 to 10 μm for the C60-assisted sample and to uniform particles with an average diameter of about 2 μm for the MC-assisted sample. Correspondingly, the onset temperature for dehydrogenation of NaAlH4 is reduced to about 188, 185 and 160 °C for the samples assisted with GNs, C60 and MC, respectively, much lower than 210 °C for the pristine sample. A remarkable reduction in activation energy for three-step dehydrogenation is also obtained in NaAlH4/carbon nanomaterial composites relative to the pristine sample, and the improved efficiency of carbon nanomaterials for kinetics is found to be in the order of MC > C60 > GNs. These positive improvements can be attributed to both the particle refinement and interaction between NaAlH4 and the carbon nanomaterial that are in intimate contact with each other, which are not only evidenced by FE-SEM observation, but also supported by 27Al solid-state NMR characterization.

Hydrogen-induced magnesium–zirconium interfacial coupling: enabling fast hydrogen sorption at lower temperatures

The implementation of magnesium (Mg) as a hydrogen-storage medium has long been restricted because of its rather sluggish hydrogen sorption at high temperatures. Here, we report a method for using hydrogen-induced Mg–Zr interfacial coupling to manipulate the migration of hydrogen atoms and thus tune their uptake and release in a micrometer-sized Mg-rich composite. The associated Mg–Zr–H interfaces were assembled in situ by high-pressure ball milling and isothermal treatment of MgH2 and Zr powders under a hydrogen atmosphere. The interfaces gradually disintegrated upon MgH2 desorption but also recovered their original compositions upon absorption while the ZrH2 originating from Zr hydrogenation remained completely unchanged. Compared to pure MgH2, the hydrogen sorption of the Mg–Zr–H composite was thus shown to be dramatically faster at lower temperatures, whereby it not only absorbed hydrogen close to saturation at 100 °C within 2 h, while the pure Mg did not absorb hydrogen at all, but also started to release hydrogen at ∼235 °C with a reduction in the activation energy of desorption by ∼40 kJ mol−1. These remarkable enhancements cannot be explained by the decrease in the size of the MgH2 grains alone but are most likely due to the introduction of Mg–Zr–H interfaces and large fractions of defects that provide channels for facile hydrogen dissociation and migration into the Mg/MgH2 matrix.

Embedding ZnSe nanodots in nitrogen-doped hollow carbon architectures for superior lithium storage

Transition metal chalcogenides represent a class of the most promising alternative electrode materials for high-performance lithium-ion batteries (LIBs) owing to their high theoretical capacities. However, they suffer from large volume expansion, particle agglomeration, and low conductivity during charge/discharge processes, leading to unsatisfactory energy storage performance. In order to address these issues, we rationally designed three-dimensional (3D) hybrid composites consisting of ZnSe nanodots uniformly confined within a N-doped porous carbon network (ZnSe ND@N-PC) obtained via a convenient pyrolysis process. When used as anodes for LIBs, the composites exhibited outstanding electrochemical performance, with a high reversible capacity (1,134 mA·h·g−1 at a current density of 600 mA·g−1 after 500 cycles) and excellent rate capability (696 and 474 mA·h·g−1 at current densities of 6.4 and 12.8 A·g−1, respectively). The significantly improved lithium storage performance can be attributed to the 3D architecture of the hybrid composites, which not only mitigated the internal mechanical stress induced by the volume change and formed a 3D conductive network during cycling, but also provided a large reactive area and reduced the lithium diffusion distance. The strategy reported here may open a new avenue for the design of other multifunctional composites towards high-performance energy storage devices.

Facile self-assembly of light metal borohydrides with controllable nanostructures

Herein, a self-assembly strategy for the realization of diverse light metal complex borohydride nanoparticles (NPs) with sphere, polygon and hollow geometries is presented. Under ambient conditions, the particle sizes of the LiBH4 NPs formed can easily be controlled by varying the concentration which enables hydrogen gas release at ∼72 °C.

Advanced H2-storage system fabricated through chemical layer deposition in a well-designed porous carbon scaffold

A new and effective in situ impregnation/deposition technique of chemical layer deposition (CLD) on a gas–solid interface is developed for fast and controllable film deposition and functional nanostructure design. Using CLD, a series of nanostructured Al(BH4)3(NH3)6@porous carbon composites are successfully produced, and a significant improvement of the hydrogen storage properties of Al(BH4)3(NH3)6 is achieved with tunable dehydrogenation temperature ranging from 114 to 175 °C, enhanced dehydrogenation kinetics with a low activation energy of 65.6 KJ mol−1 compared to 105.5 KJ mol−1 for the bulk counterpart, and a significantly increased H2 purity from 67.4% to 93.5%.

Synthesis of Ammonia Borane Nanoparticles and the Diammoniate of Diborane by Direct Combination of Diborane and Ammonia.

Pure nanoparticle ammonia borane (NH3 BH3 , AB) was first prepared through a solvent-free, ambient-temperature gas-phase combination of B2 H6 with NH3 . The prepared AB nanoparticle exhibits improved dehydrogenation behavior giving 13.6u2005wt.u2009% H2 at the temperature range of 80-175u2009°C without severe foaming. Ammonia diborane (NH3 BH2 (μ-H)BH3 , AaDB) is proposed as the intermediate in the reaction of B2 H6 with NH3 based on theoretical studies. This method can also be used to prepare pure diammoniate of diborane ([H2 B(NH3 )2 ][BH4 ], DADB) by adjusting the ratio and concentration of B2 H6 to NH3 .

CuGaS2 nanoplates: a robust and self-healing anode for Li/Na ion batteries in a wide temperature range of 268–318 K

The practical application of batteries in electric vehicles (EVs) and hybrid electric vehicles (HEVs) is hindered by the narrow operating temperature range due to the degradation of the solid–electrolyte interface (SEI) layer at high temperature and poor ion/electron diffusion kinetics at low temperature. Herein, we firstly report CuGaS2 hexagonal nanoplates as a novel and robust anode material working in a wide temperature range. CuGaS2 nanoplates with a lateral size of 2–3 μm and thickness of 180–200 nm have been successfully synthesized by a vapor thermal transformation from the oxide counterpart CuGaO2. The thermal workability of the as-synthesized CuGaS2 benefits from a synergistic effect including the high conductivity of copper and the self-healing nature of liquid metal gallium. Room temperature CuGaS2 as a lithium ion battery anode electrode exhibits a high reversible capacity over 521 mA h g−1 after 600 cycles at a high current density of 5 A g−1. Furthermore, as the temperature is lifted to 318 K, the CuGaS2 electrode exhibits a stable and reversible capacity over 784 mA h g−1 at a high current density of 0.5 A g−1; even at the low temperature of 268 K, a reversible capacity over 407 mA h g−1 can be realized, which is much superior to that of the commercial graphite anode.