Suppressing Universal Cathode Crossover in High-Energy Lithium Metal Batteries via a Versatile Interlayer Design.

The universal cathode crossover such as chemical and oxygen has been significantly overlooked in lithium metal batteries using high-energy cathodes which leads to severe capacity degradation and raises serious safety concerns. Herein, a versatile and thin (≈25 µm) interlayer composed of multifunctional active sites was developed to simultaneously regulate the Li deposition process and suppress the cathode crossover. The as-induced dual-gradient solid-electrolyte interphase combined with abundant lithiophilic sites enable stable Li stripping/plating process even under high current density of 10 mA cm-2 . Moreover, X-ray photoelectron spectroscopy and synchrotron X-ray experiments revealed that N-rich framework and CoZn dual active sites can effectively mitigate the undesired cathode crossover, hence significantly minimizing Li corrosion. Therefore, assembled lithium metal cells using various high-energy cathode materials including LiNi0.7 Mn0.2 Co0.1 O2 , Li1.2 Co0.1 Mn0.55 Ni0.15 O2 , and sulfur demonstrate significantly improved cycling stability with high cathode loading.

Pushing Lithium-Sulfur Batteries towards Practical Working Conditions through a Cathode-Electrolyte Synergy.

The commercialization of lithium-sulfur (Li-S) batteries is still hindered by the unsatisfactory cell performance under practical working conditions, which is mainly caused by the sluggish cathode redox kinetics, severe polysulfide shuttling, and poor Li stripping/plating reversibility. Herein, we report an effective strategy by combining Se-doped S hosted in an ordered macroporous framework with a highly fluorinated ether (HFE)-based electrolyte to simultaneously address the aforementioned issues in both cathode and anode. A reversible and stable high areal capacity of >5.4 mAh cm-2 with high Coulombic efficiency >99.2 % can be achieved under high areal Se/S loading (5.8 mg cm-2 ), while the underlying mechanism was further revealed through synchrotron X-ray probes and Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS). The practical application potential was further evaluated at low (0 °C) and high (55 °C) temperatures under high areal Se/S loading (>5.0 mg cm-2 ) and thin Li metal (40 µm).

Resonance-Frequency Modulation for Rapid, Point-of-Care Ebola-Glycoprotein Diagnosis with a Graphene-Based Field-Effect Biotransistor.

Recent outbreaks of Ebola-virus infections in several countries demand a rapid point-of-care (POC)-detection strategy. This paper reports on an innovative pathway founded on electronic-resonance-frequency modulation to detect Ebola glycoprotein (GP), on the basis of a carrier-injection-trapping-release-transfer mechanism and the standard antibody-antigen-interaction principle within a dielectric-gated reduced graphene oxide (rGO) field-effect transistor (GFET). The sensitivity of Ebola detection can be significantly enhanced by monitoring the device's electronic-resonance frequency, such as its inflection frequency ( fi), where the phase angle reaches a maximum (θmax). In addition to excellent selectivity, a sensitivity of ∼36-160% and ∼17-40% for 0.001-3.401 mg/L Ebola GP can be achieved at high and low inflection-resonance frequencies, respectively, which are several orders of magnitude higher than the sensitivity from other electronic parameters (e.g., resistance-based sensitivity). Using equivalent circuit modeling for contributions from channel and contact, analytical equations for resonance shifts have been generalized. When matching with the incoming ac-measurement signal, electronic resonance from the phase-angle spectrum evolves from various relaxation processes (e.g., trap and release of injected charges at surface-trap sites of the channel-gate oxide and channel-source or drain interfaces) that are associated with a characteristic emission frequency. Using charge-relaxation dynamics, a high-performance bio-FET sensing platform for healthcare and bioelectronic applications is realized through resonance shifting.

Stabilizing MoS2 Nanosheets through SnO2 Nanocrystal Decoration for High-Performance Gas Sensing in Air.

The unique properties of MoS(2) nanosheets make them a promising candidate for high-performance room temperature sensing. However, the properties of pristine MoS(2) nanosheets are strongly influenced by the significant adsorption of oxygen in an air environment, which leads to instability of the MoS(2) sensing device, and all sensing results on MoS(2) reported to date were exclusively obtained in an inert atmosphere. This significantly limits the practical sensor application of MoS(2) in an air environment. Herein, a novel nanohybrid of SnO(2) nanocrystal (NC)-decorated crumpled MoS(2) nanosheet (MoS(2)/SnO(2)) and its exciting air-stable property for room temperature sensing of NO(2) are reported. Interestingly, the SnO(2) NCs serve as strong p-type dopants for MoS(2), leading to p-type channels in the MoS(2) nanosheets. The SnO(2) NCs also significantly enhance the stability of MoS(2) nanosheets in dry air. As a result, unlike other MoS(2) sensors operated in an inert gas (e.g. N(2)), the nanohybrids exhibit high sensitivity, excellent selectivity, and repeatability to NO(2) under a practical dry air environment. This work suggests that NC decoration significantly tunes the properties of MoS(2) nanosheets for various applications.

A hierarchical tin/carbon composite as an anode for lithium-ion batteries with a long cycle life.

Tin is a promising anode candidate for next-generation lithium-ion batteries with a high energy density, but suffers from the huge volume change (ca. 260 %) upon lithiation. To address this issue, here we report a new hierarchical tin/carbon composite in which some of the nanosized Sn particles are anchored on the tips of carbon nanotubes (CNTs) that are rooted on the exterior surfaces of micro-sized hollow carbon cubes while other Sn nanoparticles are encapsulated in hollow carbon cubes. Such a hierarchical structure possesses a robust framework with rich voids, which allows Sn to alleviate its mechanical strain without forming cracks and pulverization upon lithiation/de-lithiation. As a result, the Sn/C composite exhibits an excellent cyclic performance, namely, retaining a capacity of 537 mAh g(-1) for around 1000 cycles without obvious decay at a high current density of 3000 mA g(-1) .

High-Power-Density, High-Energy-Density Fluorinated Graphene for Primary Lithium Batteries.

Li/CFx is one of the highest-energy-density primary batteries; however, poor rate capability hinders its practical applications in high-power devices. Here we report a preparation of fluorinated graphene (GFx) with superior performance through a direct gas fluorination method. We find that the so-called "semi-ionic" C-F bond content in all C-F bonds presents a more critical impact on rate performance of the GFx in comparison with sp2 C content in the GFx, morphology, structure, and specific surface area of the materials. The rate capability remains excellent before the semi-ionic C-F bond proportion in the GFx decreases. Thus, by optimizing semi-ionic C-F content in our GFx, we obtain the optimal x of 0.8, with which the GF0.8 exhibits a very high energy density of 1,073 Wh kg-1 and an excellent power density of 21,460 W kg-1 at a high current density of 10 A g-1. More importantly, our approach opens a new avenue to obtain fluorinated carbon with high energy densities without compromising high power densities.

Organometallic Precursor-Derived SnO2/Sn-Reduced Graphene Oxide Sandwiched Nanocomposite Anode with Superior Lithium Storage Capacity.

Benefiting from the reversible conversion reaction upon delithiation, nanosized SnO2, with its theoretical capacity of 1494 mA h g-1, has gained special attention as a promising anode material. Here, we report a self-assembled SnO2/Sn-reduced graphene oxide (rGO) sandwich nanocomposite developed by organometallic precursor coating and in situ transformation. Ultrafine SnO2 nanoparticles with an average diameter of 5 nm are sandwiched within the rGO/carbonaceous network, which not only greatly alleviates the volume changes upon lithiation and aggregation of SnO2 nanoparticles but also facilitates the charge transfer and reaction kinetics of SnO2 upon lithiation/delithiation. As a result, the SnO2/Sn-rGO nanocomposite exhibited a superior lithium storage capacity with a reversible capacity of 1307 mA h g-1 at a current density of 80 mA g-1 in the potential window of 0.01-2.5 V versus Li+/Li and showed a reversible capacity of 767 mA h g-1 over 200 cycles at a current density of 400 mA g-1. When cycling at a higher current density of 1600 mA g-1, the SnO2/Sn-rGO nanocomposite showed a highly stable capacity of 449 mA g-1 without obvious decay after 400 cycles.

Highly porous N-doped graphene nanosheets for rapid removal of heavy metals from water by capacitive deionization.

This work reports on a highly porous N-doped graphene-based capacitive deionization device, which exhibits a high removal efficiency (90-100%), fast removal (<30 min), and good regeneration performance (10 cycles, 99% retention) for multiple heavy metals (Pb2+, Cd2+, Cu2+, Fe2+, etc.) in water with a wide range of concentrations (0.05-200 ppm).

A high-performance catalyst support for methanol oxidation with graphene and vanadium carbonitride.

In this study, a graphene-vanadium carbonitride (G-V(C, N)) hybrid is reported as a novel support for the Pt catalyst in methanol oxidation. The catalytic activity of the Pt/G-V(C, N) hybrid for methanol oxidation is greatly enhanced compared with that of a commercial Pt/C catalyst with carbon black as the catalyst support. The outstanding catalytic activity of the Pt/G-V(C, N) catalyst suggests the potential of using graphene-metal carbonitride as the catalyst support in fuel cells.

Hydrothermal synthesis of vanadium nitride and modulation of its catalytic performance for oxygen reduction reaction.

A creative hydrothermal synthesis method followed by calcination for vanadium nitride (VN) is reported. The oxygen reduction reaction (ORR) study of the catalyst shows that VN possesses a comparable catalytic performance to commercial Pt/C catalyst. The ORR catalytic activity study of vanadium nitride, vanadium carbonitride, and vanadium carbide reveals that tuning anions offers a promising route for the activity enhancement of the non-precious metal catalysts.

Novel hybrid carbon nanofiber/highly branched graphene nanosheet for anode materials in lithium-ion batteries.

The novel hybrid carbon nanofiber (CNF)/highly branched graphene nanosheet (HBGN) is synthesized via a simple two-step CVD method and its application as the anode material in a lithium-ion battery (LIB) is demonstrated. The CNFs offer a good electrical conductivity and a robust supporting structure, while the HBGNs provide increased Li storage sites including nanoporous cavities, large surface area, and edges of exposed graphene platelets. The hybrid material showed a reversible capacity of 300 mAh g(-1) with excellent cycling stability. Our study provides a new avenue for design and synthesis of carbon-carbon hybrid materials for versatile applications.

Hierarchical nanohybrids with porous CNT-networks decorated crumpled graphene balls for supercapacitors.

One of the most challenging issues in developing supercapacitor technology is the rational design and synthesis of active electrode materials, at the nanoscale, with favorable morphologies, reasonable porous structure, and excellent conductivity. By transforming a two-dimensional (2D) graphene sheet into a crumpled ball shape, a novel three-dimensional (3D) graphene structure with a large surface area and aggregation-resistant properties has been proposed as an active material in supercapacitors to address the issues associated with the restacking of 2D graphene sheets. To further improve the mass transport/electron transfer and address the issue of limited contact spots between the crumpled graphene balls (CGBs) or between the CGBs and the current collector, we report here a unique hierarchical nanohybrid with porous carbon nanotube (CNT)-networks decorated CGBs (p-CNTn/CGBs), which not only greatly improves the affinity for bridging the active material and the current collector but also maintains favorable features for supercapacitor applications, such as a large surface area, 3D hierarchical nanostructure, excellent electrical conductivity, and outstanding aggregation-resistance. The performance established on the p-CNTn/CGBs far exceeded the bare CGB and reduced graphene oxide (RGO) counterparts in terms of specific capacitance and rate capabilities.

Multilayered Si nanoparticle/reduced graphene oxide hybrid as a high-performance lithium-ion battery anode.

Multilayered Si/RGO anode nanostructures, featuring alternating Si nanoparticle (NP) and RGO layers, good mechanical stability, and high electrical conductivity, allow Si NPs to easily expand between RGO layers, thereby leading to high reversible capacity up to 2300 mAh g(-1) at 0.05 C (120 mA g(-1) ) and 87% capacity retention (up to 630 mAh g(-1) ) at 10 C after 152 cycles.

Improved cyclic performance of Si anodes for lithium-ion batteries by forming intermetallic interphases between Si nanoparticles and metal microparticles.

Silicon, an anode material with the highest capacity for lithium-ion batteries, needs to improve its cyclic performance prior to practical applications. Here, we report on a novel design of Si/metal composite anode in which Si nanoparticles are welded onto surfaces of metal particles by forming intermetallic interphases through a rapid heat treatment. Unlike pure Si materials that gradually lose electrical contact with conductors and binders upon repeated charging and discharging cycles, Si in the new Si/metal composite can maintain the electrical contact with the current collector through the intermetallic interphases, which are inactive and do not lose physical contact with the conductors and binders, resulting in significantly improved cyclic performance. Within 100 cycles, only 23.8% of the capacity of the pure Si anode is left while our Si/Ni anode obtained at 900 °C maintains 73.7% of its capacity. Therefore, the concept of employing intermetallic interphases between Si nanoparticles and metal particles provides a new avenue to improve the cyclic performance of Si-based anodes.

Controllable synthesis of α- and ß-MnO(2): cationic effect on hydrothermal crystallization.

α- and ß-MnO(2) were controllably synthesized by hydrothermally treating amorphous MnO(2) obtained via a reaction between Mn(2+) and MnO(4)(-), and cationic effects on the hydrothermal crystallization of MnO(2) were investigated systematically. The crystallization is believed to proceed by a dissolution-recrystallization mechanism; i.e. amorphous MnO(2) dissolves first under hydrothermal conditions, then condenses to recrystallize, and the polymorphs formed are significantly affected by added cations such as K(+), NH(4)(+) and H(+) in the hydrothermal systems. The experimental results showed that K(+)/NH(4)(+) were in competition with H(+) to form polymorphs of α- and ß-MnO(2), i.e., higher relative K(+)/NH(4)(+) concentration favoured α-MnO(2), while higher relative H(+) concentration favoured ß-MnO(2).

Arrangements of four beams for any Bravais lattice.

A single geometric model based on a new concept of a reciprocal primitive pyramid (RPP) in reciprocal space is proposed for investigation of relationships between any three-dimensional (3D) lattice and arrangements of four beams (AFBs) that produce the lattice. A ternary linear equation set, described for the one-to-one correspondence between a RPP and AFB, can readily reveal all AFBs for the same lattice (AFBSLs). Quantitative AFBs for bcc and fcc real lattices are illustrated to show that various AFBSLs can modulate the properties of a photonic bandgap (PBG) both by tuning the lattice constant and by changing the lattice-point shape. This fact may yield the appropriate AFB for a complete 3D PBG with the desired center wavelength. The nonuniqueness of AFBSLs can provide abundant choices for persons who plan interference experiments, especially for holographic fabrication of 3D photonic crystals (PCs).