Zhian Zhang

Enhanced rate capability and cycle stability of lithium–sulfur batteries with a bifunctional MCNT@PEG-modified separator

As one of the most promising high-energy lithium batteries, the commercialization of lithium–sulfur (Li–S) batteries remains a huge challenge due to their poor rate performance and low cycle stability, which originate partly from the dissolution of polysulfides and their migration from the S cathode to the Li anode through the separator. Novel sulfur-based composite cathodes have been constantly put forward to restraint the dissolution of polysulfides; however, less attention has been paid to modifying the separator. In this work, a multi-walled carbon nanotube@polyethylene glycol (MCNT@PEG) composite is designed and prepared to modify the commercial Celgard separator. With the bifunctional MCNT@PEG-modified separator, Li–S cells possess a high initial discharge capacity of 1283 mA h g−1 at 0.5 C and undertake a long charge/discharge process of 500 cycles at 1 C with 0.12% capacity fading per cycle. Moreover, when the rate is increased to 5 C, the cells can also deliver a discharge capacity of 657 mA h g−1. These encouraging electrochemical results highlight the excellent rate capability and high cycle stability of Li–S cells, which could be attributed to the strong chemical and physical absorption properties and high electron conductivity of the MCNT@PEG layer. This facile approach to restrain the shuttle effect of polysulfides makes further progress in obtaining the enhanced performance of Li–S batteries.

Sulfur encapsulated in a TiO2-anchored hollow carbon nanofiber hybrid nanostructure for lithium-sulfur batteries.

A hollow carbon nanofiber hybrid nanostructure anchored with titanium dioxide (HCNF@TiO2) was prepared as a matrix for effective trapping of sulfur and polysulfides as a cathode material for Li-S batteries. The synthesized composites were characterized and examined by X-ray diffraction, nitrogen adsorption-desorption measurements, field-emission scanning electron microscopy, scanning transmission electron microscopy, and electrochemical methods such as galvanostatic charge/discharge, rate performance, and electrochemical impedance spectroscopy tests. The obtained HCNF@TiO2-S composite showed a clear core-shell structure with TiO2 nanoparticles coating the surface of the HCNF and sulfur homogeneously distributed in the coating layer. The HCNF@TiO2-S composite exhibited much better electrochemical performance than the HCNF-S composite, which delivered an initial discharge capacity of 1040 mA h g(-1) and maintained 650 mAh g(-1) after 200 cycles at a 0.5 C rate. The improvements of electrochemical performances might be attributed to the unique hybrid nanostructure of HCNF@TiO2 and good dispersion of sulfur in the HCNF@TiO2-S composite.

Mesoporous carbon from biomass: one-pot synthesis and application for Li–S batteries

A new one-pot and activation-free method was developed to synthesize high porosity biomass-derived carbon (HPBC) with uniform mesopores through sol–gel route. The as-prepared HPBC material possesses high surface area up to 949.85 m2 g−1 and high pore volume of 3.14 cm3 g−1. Cathodes with sulfur content of 81.29 wt% for Li–S batteries were prepared using the HPBC as a conductive matrix and a certain amount of space was preserved to accommodate the volume change during lithiation. When evaluated for electrochemical properties, the uniform pore structure of the HPBC afforded superior cyclability and rate performance for the Li–S batteries. An initial capacity of 922 mA h g−1 and a reversible capacity of 683 mA h g−1 were delivered after 100 cycles at a current density of 0.5 C. Specifically, a reversible capacity of 483 mA h g−1 was retained over 300 cycles at a current density of 1 C.

Confining selenium in nitrogen-containing hierarchical porous carbon for high-rate rechargeable lithium–selenium batteries

A novel nitrogen-containing hierarchical porous carbon (NCHPC) was prepared by a simple template process and chemical activation and a selenium/carbon composite based on NCHPC was synthesized for lithium–selenium batteries by a melt-diffusion method. The Se–NCHPC composite was characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (SEM), and transmission electron microscopy (TEM) measurements. It is found that the elemental selenium was dispersed inside the hierarchical pores of NCHPC. It is demonstrated from cyclic voltammetry (CV) and galvanostatic discharge–charge processes that the Se–NCHPC composite has a large reversible capacity and high rate performance as cathode materials. The Se–NCHPC composite with a selenium content of 56.2 wt% displays an initial discharge capacity of 435 mA h g−1 and a reversible discharge capacity of 305 mA h g−1 after 60 cycles at a 2 C charge–discharge rate. In particular, the Se–NCHPC composite presents a long electrochemical stability at a high rate of 5 C. The results reveal that the electrochemical reaction constrained inside the interconnected macro/meso/micropores of NCHPC would be the dominant factor for the enhancement of the high rate performance of the selenium cathode, and the nitrogen-containing hierarchical porous carbon network would be a promising carbon matrix structure for lithium–selenium batteries.

A simple SDS-assisted self-assembly method for the synthesis of hollow carbon nanospheres to encapsulate sulfur for advanced lithium–sulfur batteries

The hollow carbon nanospheres (HCNSs) were prepared using a simple SDS-assisted self-assembly method, and a sulfur–carbon composite based on HCNSs was synthesized for lithium–sulfur batteries by a vapor phase infusion method. The sulfur–HCNS composite was characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (SEM), transmission electron microscopy (TEM), and thermogravimetry (TG) measurements. It is found that the elemental sulfur was dispersed inside the pores of carbon spheres. It is demonstrated from the galvanostatic discharge–charge process and cyclic voltammetry (CV) that the sulfur–HCNS composite has a large reversible capacity and an excellent cycling performance as cathode materials. The sulfur–HCNS composite with a sulfur content of 47.6 wt% displays an initial discharge capacity of 1031 mA h g−1 and a reversible discharge capacity of 477 mA h g−1 after 100 cycles at 0.5 C charge–discharge rate.

High performance lithium sulfur batteries with a cassava-derived carbon sheet as a polysulfides inhibitor

A biomass derived carbon material is obtained by simple carbonization of cassava and it is used to prepare a carbon sheet as an interlayer for Li–S batteries. The as-prepared carbon sheet possesses macroporous structure and high conductivity, which is in favor of electrolyte permeation and helps to accelerate the electrochemical kinetics. The cell with the as-prepared interlayer shows superior rate performance and cyclability. Even at an ultrahigh rate (4 C, 1 C = 1675 mA h gsulfur−1), a discharge capacity of 640 mA h g−1 is still retained for the cell. Meanwhile, the cell with the as-prepared interlayer exhibits a superior reversible capacity of 811 mA h g−1 after 100 cycles at 0.5 C, and the discharge capacity retention is over 62%. The excellent electrochemical property probably is attributed to the high conductivity and macroporous structure of the as-prepared interlayer, which contribute to the accommodation of migrating polysulfides accelerating the transfer of electrons and ions, and consequently, enhancing the electrochemical reactivity of the cathode as well as suppressing the formation of the Li2S layer on the cathode.

ZnS nanoparticles embedded in porous carbon matrices as anode materials for lithium ion batteries

In situ synthesis of a novel zinc sulfide/porous carbon composite (ZnS/PC) with ZnS nanoparticles finely embedded in porous carbon matrices is achieved by virtue of the metal–organic frameworks (MOFs) strategy. The as-obtained ZnS/PC exhibits significant electrochemical performance as an anode material for lithium ion batteries.

Improvement of electrochemical performance of rechargeable lithium–selenium batteries by inserting a free-standing carbon interlayer

A simple, low-cost modification of lithium–selenium (Li–Se) cells by placing a carbon interlayer between the selenium electrode and the separator has been investigated to significantly improve the electrochemical performance of Li–Se cells.

Growth and Characterization of Cu2ZnSnS4 Thin Films by DC Reactive Magnetron Sputtering for Photovoltaic Applications

Cu 2 ZnSnS 4 (CZTS) thin films were grown by a dc reactive magnetron sputtering technique and characterized by studying their composition, structural, optical, and electrical properties. Raman and X-ray diffraction analyses confirm the formation of quaternary Cu 2 ZnSnS 4 phase with strong preferential orientation along the (112) plane and the presence of minor secondary phases Cu 2-x S and Cu 3 SnS 4 . The grown CZTS film with a homogeneous morphology demonstrates an optical absorption coefficient of higher than 10 5 cm -1 and an optical bandgap of 1.50 ± 0.01 eV. All samples are p-type and exhibit high carrier concentration in the order of 10 18 cm -3 and low carrier mobility.

Electrodeposition of Cobalt Selenide Thin Films

Cobalt selenide thin films have been prepared onto tin oxide glass substrates by electrodeposition potentiostatically from an aqueous acid bath containing H 2 SeO 3 and Co(CH 3 COO) 2 at 50°C. The electrodeposition mechanism was investigated by cyclic voltammetry. The morphological, compositional, structural, and optical properties of the deposited films have been studied using scanning electron microscopy, energy-dispersive X-ray spectroscopy, X-ray diffraction, and optical absorption techniques, respectively. The formation of cobalt selenide was confirmed to proceed via an underpotential deposition mechanism. Se-rich CoSe thin films with compact and homogeneous morphology and hexagonal crystal structure were obtained at a deposition potential of―0.5 V vs saturated calomel electrode. The electrodeposited CoSe film exhibits an optical absorption coefficient of higher than 10 5 cm ―1 and an optical bandgap of 1.53 ± 0.01 eV.