Wanqun Zhang

Amorphous S-rich S1−xSex/C (x ≤ 0.1) composites promise better lithium–sulfur batteries in a carbonate-based electrolyte

Polysulfide dissolution and the insulating nature of sulfur cause significant capacity fading and low efficiency in rechargeable lithium–sulfur batteries. Here, we show that these defects can be effectively diminished by immobilizing sulfur in porous carbon via the interaction of a small amount of selenium. Amorphous S-rich S1−xSex/C (x ≤ 0.1) composites have been prepared starting from Se and S powders at 260 °C. Raman spectra reveal the existence of S–Se bonds in S1−xSex/C composites. As cathodes for lithium–sulfur batteries, S1−xSex/C (x ≤ 0.1) composites exhibit high electrochemical performance in a carbonate-based electrolyte. S0.94Se0.06/C composites deliver the best performance with a capacity of 910 mA h g−1 at 1 A g−1 over 500 cycles, 1105 mA h g−1 at 0.2 A g−1 after 100 cycles and a good rate capability of 617 mA h g−1 at 20 A g−1.

A Deep Reduction and Partial Oxidation Strategy for Fabrication of Mesoporous Si Anode for Lithium Ion Batteries

A deep reduction and partial oxidation strategy to convert low-cost SiO2 into mesoporous Si anode with the yield higher than 90% is provided. This strategy has advantage in efficient mesoporous silicon production and in situ formation of several nanometers SiO2 layer on the surface of silicon particles. Thus, the resulted silicon anode provides extremely high reversible capacity of 1772 mAh g(-1), superior cycling stability with more than 873 mAh g(-1) at 1.8 A g(-1) after 1400 cycles (corresponding to the capacity decay rate of 0.035% per cycle), and good rate capability (∼710 mAh g(-1) at 18A g(-1)). These promising results suggest that such strategy for mesoporous Si anode can be potentially commercialized for high energy Li-ion batteries.

Synthesis of nanocrystalline NiS with different morphologies

Abstract Millerite NiS nanocrystals have been prepared through the solvent (hydro-) thermal method. The XRD patterns indicated that the products were pure millerite NiS with cell parameters a =9.624(4) A, c =3.150(1) A. Using ethylenediamine and hydrazine hydrate as solvent resulted in the formation of rod-like nanocrystalline NiS, whereas spherical nanoparticles were obtained using aqueous ammonia as solvent. The products obtained have relatively high surface areas, which favors the application in catalysis.

SnS2- Compared to SnO2-Stabilized S/C Composites toward High-Performance Lithium Sulfur Batteries

The common sulfur/carbon (S/C) composite cathodes in lithium sulfur batteries suffer gradual capacity fading over long-term cycling incurred by the poor physical confinement of sulfur in a nonpolar carbon host. In this work, these issues are significantly relieved by introducing polar SnO2 or SnS2 species into the S/C composite. SnO2- or SnS2-stabilized sulfur in porous carbon composites (SnO2/S/C and SnS2/S/C) have been obtained through a baked-in-salt or sealed-in-vessel approach at 245 °C, starting from metallic tin (mp 231.89 °C), excess sulfur, and porous carbon. Both of the in situ-formed SnO2 and SnS2 in the two composites could ensure chemical interaction with lithium polysulfide (LiPS) intermediates proven by theoretical calculation. Compared to SnO2/S/C, the SnS2/S/C sample affords a more appropriate binding effect and shows lower charge transfer resistance, which is important for the efficient redox reaction of the adsorbed LiPS intermediates during cycling. When used as cathodes for Li-S batteries, the SnS2/S/C composite with sulfur loading of 78 wt % exhibits superior electrochemical performance. It delivers reversible capacities of 780 mAh g(-1) after 300 cycles at 0.5 C. When further coupled with a Ge/C anode, the full cell also shows good cycling stability and efficiency.

A solvothermal route to wurtzite ZnSe nanoparticles

Zinc powder reacts with equivalent elemental selenium in solvent ethylenediamine at 120 °C for 6 h to form a complex, which is converted to ZnSe nanoparticles by pyrolysis or protonization. X-ray diffraction results suggest that the as-formed products have wurtzite structure. Transmission electron microscopy observation show that particles with spherical and laminar morphology were produced by pyrolysis and protonization, respectively. The formation of ZnSe nanoparticles is also investigated by infrared and thermal analysis.

A convenient hydrothermal route to mineral Ag3CuS2 nanorods

Abstract A convenient hydrothermal route is proposed for synthesizing mineral Ag3CuS2 nanorods. X-ray powder diffraction (XRD) patterns indicated the formation of Ag3CuS2, and elemental analysis and X-ray photoelectron spectra (XPS) revealed the stoichiometric relation between Ag, Cu, and S. Transmission electron microscope (TEM) images demonstrated that the final product consisted of nanorods with diameters from 30 to 150 nm and lengths from 200 nm to 1 μm. A possible formation mechanism of Ag3CuS2 nanorods was proposed.

A Composite Structure of Cu3Ge/Ge/C Anode Promise Better Rate Property for Lithium Battery

Much effort has been made to search for high energy and high power density electrode materials for lithium ion batteries. Here, a composite structure among Ge, C and Cu3Ge in Cu3Ge/Ge/C materials with a high rate performance of lithium batteries has been reported. Such Cu3Ge/Ge/C composite is synthesized through the in-situ formation of Ge, C and Cu3Ge by one-pot reaction. Density function theory (DFT) calculations and electrochemical impedance spectroscopy (EIS) suggest a higher electron mobility of the hibrid Cu3Ge/Ge/C composites through the in-situ preparation. As a result, remarkable charge rate over 300 C (fast delithiated capability) and outstanding cycling stability (≈0.02% capacity decay per cycle for 500 cycles at 0.5 C) are achieved for the Cu3Ge/Ge/C composites anode. These Cu3Ge/Ge/C composites demonstrate another perspective to explore the energy storage materials and should provide a new pathway for the design of advanced electrode materials.

Synthesis of NiS2-xSex solid solution via an ultrasonic solvothermal route

Abstract NiS 2− x Se x solid solution has been successfully prepared via an ultrasonic solvothermal route. The products were characterized by X-ray diffraction, ICP-AES and X-ray photoelectron spectroscopy. It has been found that the lattice parameter a follows a Vegard law with the selenium content x Se . The effects of ultrasonic and solvent on synthesizing NiS 2− x Se x solid solution were discussed. By comparing the Se molar fraction in the reagents to the selenium content in the samples, the formation mechanism of NiS 2− x Se x solid solution was proposed. Scanning electron microscopy images indicate that the products exhibit different morphologies corresponding to different compositions.

A facile synthesis of highly porous CdSnO3 nanoparticles and their enhanced performance in lithium-ion batteries

CdSnO3 materials have been extensively studied as gas-sensing materials. However, there are few reports on the synthesis and use of porous CdSnO3 nanostructures for energy storage. Herein, we report highly porous CdSnO3 nanoparticles prepared using citric acid with sizes in the range of ∼7.8 nm to 28.7 nm and the application of these nanoparticles as an anode material for rechargeable Li-ion batteries (LIBs). Electrochemical measurements showed that the highly porous CdSnO3 nanoparticles delivered a high reversible capacity of ∼515 mA h g−1 for up to 40 cycles at a current rate of 70 mA g−1. Even at a high rate of 150 mA g−1, the porous CdSnO3 could still deliver a capacity of 506 mA h g−1. It is observed that the electrochemical performance of the highly porous CdSnO3 nanoparticles is much better than that (∼370 mA h g−1 for up to 40 cycles) of a counterpart obtained without citric acid, which also demonstrates the capacity enhancement and high rate capacity.

Facile synthesis and electrochemistry of a new cubic rocksalt LixVyO2 (x = 0.78, y = 0.75) electrode material

A new phase, Li0.78V0.75O2, was fabricated for the first time on a large scale using a simple hydrothermal method. The structure of Li0.78V0.75O2 was identified by Rietveld refinement of the powder X-ray diffraction (XRD) data. XRD identified that the new Li–V–O compound had a cubic rocksalt structure, in which Li and V were evenly distributed on the octahedral sites in a cubic closely packed lattice of oxygen ions. Li0.78V0.75O2 showed structural evolution from cubic symmetry to thermodynamically stable rhombohedral symmetry LixVyO2 above 800 °C. Furthermore, the electrochemical performance of the as-prepared Li0.78V0.75O2 as an anode for Li-ion batteries was studied for the first time. Galvanostatic battery testing showed that the Li0.78V0.75O2 electrode exhibited a large reversible capacity, high rate performance and excellent cycling stability. A reversible capacity of 575 mA h g−1 was maintained even after 500 cycles at a current density of 500 mA g−1. Ex situ XRD and XPS studies on the lithiation mechanism of Li0.78V0.75O2 consistently suggested that two single-phase insertion-type lithiation processes proceed during the early stages of lithiation. Hence, a single-phase conversion reaction is followed, along with structural integration. The improved electrochemical performance can be ascribed to the unusual conversion-type lithiation process, which is not consistent with the intercalation process of LixVyO2 reported previously. More importantly, the lithiation and delithiation behavior suggests that the oxidation of V(II) to V(IV) upon cycling produces more suitable sites for Li+ insertion, which contributes to the enhanced specific capacity.