Lianbang Wang

CNx nanotubes with pyridinelike structures: p-type semiconductors and Li storage materials

Using density functional theory (DFT) computations, we investigated pyridinelike structures in a series of single-walled CN(x) nanotubes and found that tube chirality and diameter play important roles in the formation of pyridinelike structures. Not pyridinelike structures but more N(C) defects (N atoms substituting for C atoms) should be responsible for the experimentally observed donor states of CN(x) nanotubes. The adsorption energies of Li at the pyridinelike defect are so large and the energy barrier for lithium penetrating the defect is so low that CN(x) nanotubes with pyridinelike structures have enhanced capability for lithium storage.

Do Transition Metal Carbonates Have Greater Lithium Storage Capability Than Oxides? A Case Study of Monodisperse CoCO3 and CoO Microspindles

As substitutions for transition metal oxides (MOs), transition metal carbonates (MCO3) have been attracting more and more attention because of their lithium storage ability in recent years. Is MCO3 better than MOs for lithium storage? To answer this question, monodisperse CoCO3 and CoO microspindles with comparable structures were synthesized and investigated as a case study. Excluding its structural effect, we found CoCO3 still exhibited reversible capacities and rate capabilities much higher than those of CoO. The reversible capacity of CoCO3 after 10 cycles was 1065 mAh g(-1), 48.2% higher than that (∼720 mAh g(-1)) of CoO. Furthermore, the greatly different electrochemical behaviors were investigated by analyzing the discharge-charge profiles, cyclic voltammetry curves, and Nyquist plots in depth. This work can improve our understanding of the lithium storage advantages of MCO3 against MOs and enlighten us in terms of developing high-performance MCO3 with favorable structures.

Micro/nano-complex-structure SiOx–PANI–Ag composites with homogeneously-embedded Si nanocrystals and nanopores as high-performance anodes for lithium ion batteries

The extremely large volume variation and poor electronic conductivity of Si anode materials for lithium ion batteries have seriously hampered their performances and practical applications. SiOx materials are regarded as ideal alternatives to high-capacity Si anode materials for Li-ion batteries, since the generated Li2O matrix from Li–SiOx reactions can effectively accommodate the large volume swing of Si. Furthermore, micron-sized particles with much smaller surface area always present higher initial coulombic efficiency and tap density than nanomaterials. Based on the above considerations, SiOx microparticles with homogeneously-embedded Si nanocrystals and nanopores were fabricated by magnesiothermic reduction in this work and were further modified by high-electronic-conductivity and flexible polyaniline (PANI)–Ag shell. Profiting from these favorable features, the obtained SiOx–PANI–Ag micron-composites exhibited better cycling performances (with a reversible capacity of 1149 mA h g−1 after 100 cycles), good initial coulombic efficiency and tap density in comparison with SiOx-based materials in other works. This study promotes us to exploit advanced Si- or Sn-based materials for Li ion batteries and preparing micro/nano complex structures for promising applications.

Facile synthesis of MoS2/graphene composites: effects of different cationic surfactants on microstructures and electrochemical properties of reversible lithium storage

MoS2/graphene composites were synthesized through the concurrent reducing of (NH4)2MoS4 and graphene oxide sheets with assistance of different cationic surfactants (DTAB, OTAB and TBAB) followed by heat treatment in a nitrogen atmosphere. The effects of the three cationic surfactants on the microstructures and electrochemical performances of the composites for reversible lithium storage were investigated. The MoS2 in the composites prepared with assistance of DTAB or OTAB displays single-/few-layer structure, while the layered MoS2 sheets with about 6–7 layers are observed in the composite prepared with assistance of TBAB. The former two composites exhibit greatly enhanced electrochemical performance for reversible Li+ storage. In particular, MoS2/graphene composite prepared with assistance of OTAB delivered a high reversible capacity of 1056 mA h g−1 with excellent cycle stability and good rate capability. The significant improvement in the electrochemical performances is attributed to the roubest composite structure and the synergistic interactions between graphene and single-/few-layer MoS2. This work also presented a facile process to prepare MoS2/graphene composites, in which the layer number of MoS2 sheets could be adjusted to a certain extent by using different cationic surfactants.

Preparation and lithium storage performance of yolk–shell Si@void@C nanocomposites

Yolk-shell Si@void@C nanocomposites are prepared via a facile method of resorcinol-formaldehyde coating and LiOH etching, without SiO2 pre-modification on Si particles, expensive carbon sources, or environmentally-unfriendly HF solutions. Profiting from these favorable features, Si@void@C nanocomposites exhibit considerable reversible capacities (628 mA h g(-1) after 100 cycles) and good rate performances.

Multi-yolk–shell SnO2/Co3Sn2@C Nanocubes with High Initial Coulombic Efficiency and Oxygen Reutilization for Lithium Storage

The challenging problems of SnO2 anode material for lithium ion batteries are the poor electronic conductivity and the low oxygen reutilization due to the irreversibility of Li2O generated in the initial discharge leading to a theoretical initial Coulombic efficiency (ICE) of only 52.4%. Different from these strategies, this work proposes a novel strategy to level up the oxygen reutilization in SnO2 by introducing Co3Sn2 nanoalloys which can release Co atoms to reversibly react with Li2O instead. According to this protocol, multi-yolk-shell SnO2/Co3Sn2@C nanocubes are designed and successfully prepared using hollow CoSn(OH)6 nanocubes as precursors followed a hydrothermal carbon coating and calcination treatment. The unique multi-yolk-shell nanostructure offers adequate breathing space for the volumetric deformation during long-term cycling. Moreover, the removal of Li2O allows a high electronic conductivity and resultant rate performance. As a result, the efficient reutilization of oxygen enables a high ICE of 71.7% and a reversible capacity of 1003 mA h g-1 after 200 cycles at 100 mA g-1. Cyclic voltammetry, cycling performance at different voltage windows, and X-ray photoelectron spectroscopy confirm the proposed mechanism. This strategy employing oxygen-poor metals or alloys provides a novel approach to enhance the oxygen reutilization in SnO2 for higher reversibility.

Electrochemical Characteristics of LaNi4.5Al0.5 Alloy Used as Anodic Catalyst in a Direct Borohydride Fuel Cell

Abstract Fuel cells using borohydride as the fuel have received much attention because of high energy density and theoretical working potential. In this work, LaNi4.5Al0.5 hydrogen storage alloy used as the anodic material has been investigated. It was found that the increasing operation temperature was helpful to the open-circuit potential, the discharge potential and the power density, but showed a negative effect on the utilization of the fuel due to the accelerated hydrogen evolution. The high KOH concentration was favorable for high-rate discharge capability. The adsorption and transformation of hydrogen on LaNi4.5Al0.5 alloy electrode has been observed, but its contribution to the discharge capability during a high-rate discharge was small.

Uniform core–shell Cu6Sn5@C nanospheres with controllable synthesis and excellent lithium storage performances

Metallic tin (Sn) is one of the most promising alternatives to graphite anodes for lithium ion batteries due to its higher theoretical capacity, higher packing density and safer thermodynamic potential, while the huge volume transformation during repeated cycling leads to rapid pulverization and consequently poor capacity retention. This work provides an easy-to-control method to prepare uniform core–shell Cu6Sn5@C nanospheres in which Cu@Sn cores (40–50 nm in diameter) are well encapsulated by PANI-derived carbon layers with a thickness of ∼5 nm. The obtained Cu6Sn5@C exhibits an excellent cycling ability and good rate capabilities. Both the reversible capacity (518 mA h g−1) after 100 cycles and the initial coulombic efficiency (89.2%) are the highest values in Cu6Sn5-based materials. The impressive cycling performance is believed to result from the carbon coating that not only prevents particle agglomeration during the synthesis but also accommodates the vast structural transformation of the Cu6Sn5 nanocores during the electrochemical (de)lithiation process, so ensuring good ionic and electronic transport to the core. The effect of synthesis conditions on the composition are also investigated systematically.

EG-Assisted synthesis and electrochemical performance of ultrathin carbon-coated LiMnPO 4 nanoplates as cathodes in lithium ion batteries

Ultrathin carbon-coated LiMnPO4 (ULMP/C) nanoplates were prepared through an ethylene glycol- (EG-) assisted pyrolysis method. Different from most of LiMnPO4/Cworks, the obtained ULMP/C possessed relatively small particle size (less than 50nm in thickness) and preferable carbon coating (∼1nmin thickness, 2wt.%). As a reference, LiMnPO4/C (LMP/C) composites were also fabricated via the traditional hydrothermal method. X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDS), thermogravimetric analysis (TG), galvanostatic charge-discharge, and cyclic voltammetry (CV) were performed to characterize the crystalline phase, morphology, structure, carbon content, and electrochemical behaviors of samples. The electrochemical performance of bare and carbon-coated LiMnPO4 was evaluated as cathodes in lithium ion batteries. As a result, the obtained ULMP/C nanoplates demonstrated much higher reversible capacities (110.9mAhg-1 after 50 cycles at 0.1 C) and rate performances than pure LMP and LMP/C composites. This facile and efficient EG-assisted pyrolysis method can enlighten us on exploiting advanced routes to modify active materials with ultrathin and homogeneous carbon layers.