Qingshan Kong

Synthesis of Nitrogen-Doped MnO/Graphene Nanosheets Hybrid Material for Lithium Ion Batteries

Nitrogen-doped MnO/graphene nanosheets (N-MnO/GNS) hybrid material was synthesized by a simple hydrothermal method followed by ammonia annealing. The samples were systematically investigated by X-ray diffraction analysis, Raman spectroscopy, X-ray photoelectron spectroscopy, transmission electron microscopy, and atomic force microscopy. N-doped MnO (N-MnO) nanoparticles were homogenously anchored on the thin layers of N-doped GNS (N-GNS) to form an efficient electronic/ionic mixed conducting network. This nanostructured hybrid exhibited a reversible electrochemical lithium storage capacity as high as 772 mAh g(-1) at 100 mA g(-1) after 90 cycles, and an excellent rate capability of 202 mA h g(-1) at a high current density of 5 A g(-1). It is expected that N-MnO/GNS hybrid could be a promising candidate material as a high capacity anode for lithium ion batteries.

Renewable and Superior Thermal-Resistant Cellulose-Based Composite Nonwoven as Lithium-Ion Battery Separator

A renewable and superior thermal-resistant cellulose-based composite nonwoven was explored as lithium-ion battery separator via an electrospinning technique followed by a dip-coating process. It was demonstrated that such nanofibrous composite nonwoven possessed good electrolyte wettability, excellent heat tolerance, and high ionic conductivity. The cells using the composite separator displayed better rate capability and enhanced capacity retention, when compared to those of commercialized polypropylene separator under the same conditions. These fascinating characteristics would endow this renewable composite nonwoven a promising separator for high-power lithium-ion battery.

Sustainable, heat-resistant and flame-retardant cellulose-based composite separator for high-performance lithium ion battery

A sustainable, heat-resistant and flame-retardant cellulose-based composite nonwoven has been successfully fabricated and explored its potential application for promising separator of high-performance lithium ion battery. It was demonstrated that this flame-retardant cellulose-based composite separator possessed good flame retardancy, superior heat tolerance and proper mechanical strength. As compared to the commercialized polypropylene (PP) separator, such composite separator presented improved electrolyte uptake, better interface stability and enhanced ionic conductivity. In addition, the lithium cobalt oxide (LiCoO2)/graphite cell using this composite separator exhibited better rate capability and cycling retention than that for PP separator owing to its facile ion transport and excellent interfacial compatibility. Furthermore, the lithium iron phosphate (LiFePO4)/lithium cell with such composite separator delivered stable cycling performance and thermal dimensional stability even at an elevated temperature of 120°C. All these fascinating characteristics would boost the application of this composite separator for high-performance lithium ion battery.

Preparation and li storage properties of hierarchical porous carbon fibers derived from alginic acid.

One-dimensional (1D) hierarchical porous carbon fibers (HPCFs) have been prepared by controlled carbonization of alginic acid fibers and investigated with scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, nitrogen adsorption-desorption isotherms, and electrochemical tests toward lithium storage. The as-obtained HPCFs consist of a 3D network of nanosized carbon particles with diameters less than 10 nm and exhibit a hierarchical porous architecture composed of both micropores and mesopores. Electrochemical measurements show that HPCFs exhibit excellent rate capability and capacity retention compared with commercial graphite when employed as anode materials for lithium-ion batteries. At the discharge/charge rate of 45 C, the reversible capacity of HPCFs is still as high as 80 mA h g(-1) even after 1500 cycles, which is about five times larger than that of commercial graphite anode. The much improved electrochemical performances could be attributed to the nanosized building blocks, the hierarchical porous structure, and the 1D morphology of HPCFs.

Graphene decorated with molybdenum dioxide nanoparticles for use in high energy lithium ion capacitors with an organic electrolyte

An electrode material consisting of graphene decorated with molybdenum dioxide nanoparticles (G–MoO2) is developed. The material exhibits not only a high specific capacitance but also an excellent cycling performance as well as good rate capability in lithium ion capacitors (LICs). The specific capacitance of the G–MoO2 containing 10 wt% G reaches 624.0 F g−1 at a current density of 50 mA g−1, much higher than 269.2 F g−1 for the MoO2 particles alone. Even at a current density of 1000 mA g−1, a high specific capacitance of 173.2 F g−1 is obtained. The capacitance retention remains 91.2% after 500 cycles. Moreover, G–MoO2 provides a high specific energy density of 33.2 W h kg−1 at a power density of 3000 W kg−1. The influences of the synergistic effect of nanostructured MoO2 and conducting G on the electrochemical performance of the LICs are discussed.

THERMAL DEGRADATION AND FLAME RETARDANCY OF CALCIUM ALGINATE FIBERS

Calcium alginate fibers were prepared by wet spinning of sodium alginate into a coagulating bath containing calcium chloride. The thermal degradation and flame retardancy of calcium alginate fibers were investigated with thermal gravimetry (TG), X-ray diffraction (XRD), limiting oxygen index (LOI) and cone calorimeter (CONE). The results show that calcium alginate fibers are inherently flame retardant with a LOI value of 34, and the heat release rate (HRR), total heat release (THR), CO and CO2 concentrations during combustion are much lower compared with those of viscose fibers. Calcium carbonate and calcium oxide were formed during thermal degradation of calcium alginate fibers at different temperatures. The shape of calcium alginate fibers is well kept after LOI test. The rigid combustion residue char acts as an effective barrier to the outward diffusion of flame and heat. The combustion process and flame retardant mechanism of calcium alginate fibers are also discussed.

Macroscopic single-crystal gold microflakes and their devices.

A facile, green procedure is proposed to synthesize single-crystal gold microflakes with planar area up to 10(4) mu m(2). This unprecedented dimension offers new possibilities in designing flexible conductive films with tunable strain-dependent conductivity, that can be exploited in strain/force/vibration sensing devices. By using top-down micro-/nanofabrication techniques, these materials may further find use in single-crystal electronics and plasmonic applications.

A novel assembly of LiFePO4 microspheres from nanoplates

In this work, LiFePO4 microspheres with an enhanced tap density were assembled from nanoplates via solvothermal treatment with TiN nanoparticles as a conductive connector. By altering the amount of introduced TiN nanoparticles, the morphology of the as-prepared LiFePO4 can be tailored. It is demonstrated that TiN nanoparticles favor crystal growth along the b axis by breaking the surfactant blocking barrier, which has a significant effect upon the assembly of LiFePO4 nanoplates. Enhanced electronic and ionic conductivity of a LiFePO4 electrode is confirmed by electrochemical impedance spectroscopy and linear voltage scanning methods, which are beneficial to the battery performance.

Scalable synthesis of nanometric α-Fe2O3 within interconnected carbon shells from pyrolytic alginate chelates for lithium storage

Nanostructured α-Fe2O3 with a carbon coating has advantages over commercially available graphitic anodes in lithium ion batteries, including high theoretical anodic capacity (1007 mA h g−1), low cost and environmental safety. However, parts of its merits were cancelled out by the current route used for its synthesis. For example, most of its synthesis pathways are tedious, costly, on small scale and environmentally unfriendly. By combining two naturally abundant materials (iron ions and sodium alginate) into conventional wet-spinning and pyrolysis processes, we show that α-Fe2O3 could be nanostructured and carbon-coated using a facile and yet scalable technique. The successful synthesis of nanostructured α-Fe2O3 within interconnected carbon shells strongly depends on the chelation of iron ions and alginate into “egg-box” networks and an optimized pyrolysis step. Due to an extraordinary combination of nanometric scale, improved electrical conductivity and spatial confinement of the carbon coating, the resultant materials exhibit a high lithium storage capacity (e.g. up to ∼1400 mA h g−1 at a current of 50 mA g−1 in the initial cycle) and great stability (e.g. ∼560 mA h g−1 after 600 cycles at 200 mA g−1) as well as a coulombic efficiency of 97.5%. Owing to the cost-efficient, environmentally friendly and scalable production, this synthesis may pave a highly promising way to the macroscopic preparation of α-Fe2O3/carbon hybrid materials as anodes in lithium ion batteries.

Batch Studies of Zinc(II) Ion Adsorption onto Alginic Acid Fibres

The ability of alginic acid fibres to remove Zn(II) ions from aqueous solution was investigated by batch experiments. The effect of experimental parameters including pH, agitation time, initial Zn(II) ion concentration, temperature and biosorbent dosage on the biosorption of Zn(II) ions from aqueous solution was studied. Thermodynamic studies of Zn(II) ion biosorption demonstrated the exothermic nature of the process. Kinetic studies showed that the biosorption conformed to the pseudo-second-order and intra-particle diffusion models. The Langmuir and Freundlich isotherm models provided a good fit to the experimental data. The activation energy for the biosorption process suggested that it occurred in a physical manner. Alginic acid fibres have been demonstrated to be effective marine materials for the removal of Zn(II) ions from aqueous solution.