Yanhong Yin

MOF-Derived Cobalt-Doped ZnO@C Composites as a High-Performance Anode Material for Lithium-Ion Batteries

Cobalt (Co)-doped MOF-5s (Co-MOF-5s) were first synthesized by a secondary growth method, followed by a heat treatment to yield Co-doped ZnO coated with carbon (CZO@C). Compared with carbon-coated ZnO (ZnO@C), the doping of Co increased the graphitization degree of the carbon on the surface of CZO@C nanoparticles and enhanced the conductivity of the material. The electrochemical properties of the materials were characterized by galvanostatic discharge/charge tests. It was found that the as-synthesized CZO@C composites enabled a reversible capacity of 725 mA h g(-1) up to the 50th cycle at a current density of 100 mA g(-1), which was higher than that of ZnO@C composites (335 mA h g(-1)).

In situ synthesis of flexible elastic N-doped carbon foam as a carbon current collector and interlayer for high-performance lithium sulfur batteries

A flexible elastic N-doped carbon foam (NCF) has been successfully synthesized in situ via direct carbonization/pyrolysis of polyurethane foam, which is a facile, cost-effective and environmentally friendly method. Due to its uniform three-dimensional connected structure, its reasonable composition with N doping and its high electronic conductivity, the NCF can function as both a three-dimensional current collector and a carbon interlayer for lithium sulfur batteries. As a typical model, cathodes consisting of NCF and CNT/S were prepared. The resulting batteries deliver a large reversible capacity of 1124 mA h g−1 at 0.5C and retain a high specific capacity of 902.8 mA h g−1 after 100 cycles, with a coulombic efficiency of 98.6% throughout the cycles. Furthermore, a discharge capacity of 691.8 mA h g−1 is still attainable when the rate is increased to 2.0C. The excellent cycling performance and rate capability are contributed to the uniform flexible elastic, conductive 3D framework and good porosity, and may have great significance for large-scale commercial applications of Li–S batteries.

A novel sulfur/carbon composite for low cost lithium–sulfur batteries with high cycling stability

The lithium sulfur (Li–S) battery is a promising electrochemical system for the next generation high density rechargeable batteries having a theoretical energy density of ∼2600 W h kg−1. In spite of the intrinsic advantages, Li–S batteries currently are confronted with a variety of problems such as low specific capacity and short cycle life. In this work, a novel sulfur/carbon composite was prepared using coconut shell carbon as raw material for Li–S batteries. The structure of the composite could accommodate the volume expansion of sulfur particles and trap the dissolved polysulfide produced during the electrochemical reaction. Therefore, the composite based cell demonstrates a high initial capacity of 878 mA h g−1 at a rate of 0.1 C, and excellent cycling stability, in which a reversible capacity of 774 mA h g−1 was maintained even after 50 cycles.

Facile synthesis of MgFe2O4/C composites as anode materials for lithium-ion batteries with excellent cycling and rate performance

A MgFe2O4/C material is prepared by a sol–gel auto-combustion process followed by carbon coating with glucose as a carbon source. The obtained MgFe2O4/C sample shows remarkably enhanced specific capacity and rate performance. A reversible capacity of about 1965 mA h g−1 after 100 cycles at 0.1C (107.2 mA g−1) is obtained. Specifically, the MgFe2O4/C composite electrode delivers a reversible specific capacity of 500 mA h g−1 even at 10C (10 000 mA g−1), indicating the excellent rate capability of the MgFe2O4 electrode.

Facile synthesis of Fe2O3/MWCNT composites with improved cycling stability

In this study, Fe2O3/multi-walled carbon nanotube (Fe2O3/MWCNT) composites were synthesized via vacuum solution absorption and subsequent calcination treatment. The amount of Fe2O3 and MWCNT components, crystalline structure, morphology and electrochemical performance of the as-prepared material were characterized by thermo-gravimetric (TG) analysis, X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Brunauer–Emmett–Teller (BET) method, energy dispersive spectrometry (EDS) and charge–discharge tests. Results show that Fe2O3 nano-particles, with a diameter of about 23 nm, loaded in the void space in the intertwined MWCNT matrix or on the MWCNT homogeneously. The as-obtained Fe2O3/MWCNT composites have a relatively small BET surface area, pore size and pore volume compared to that of pure MWCNT. Electrochemical measurements show that the Fe2O3/MWCNT composites exhibit a high reversible capacity of 1026 mA h g−1 after 50 cycles at a charge–discharge rate of 0.2 C. The improved performance may be ascribed to the nano-sized Fe2O3 with a faster Li+ diffusion coefficient which can release the volume expansion effectively. On the other hand, the MWCNT can act as a buffering matrix and electron conductors in the composites.

Carbonized non-woven fabric films as adsorbing interlayers to enhance electrochemical performance of lithium–sulfur batteries

Lithium–sulfur (Li–S) batteries with an effective adsorbing interlayer, high capacity and long cycle life have been fabricated using a simple method by placing an interlayer between the sulfur cathode and the separator. The interlayer with optimized porosity, electrolyte uptake and electrical conductivity can facilitate the use of pure sulfur (with a sulfur content of 70%) as a highly reversible cathode, which was made of carbonized non-woven fabrics (Mind Act Upon Mind™ Skincare Wipes) modified with Ketjenblack. A high capacity of 1486 mA h g−1 at a rate of 0.1C (1C = 1675 mA g−1) in the first cycle was obtained, and the reversible capacity remains high, up to 858 mA h g−1, even after 100 cycles.

A particle–carbon matrix architecture for long-term cycle stability of ZnFe2O4 anode

ZnFe2O4/C with a unique compound structure was in situ synthesized through a facile one-step route using glycine as complexing agent and carbon source. ZnFe2O4 nanoparticles are embedded in a carbon matrix to form submicron particles. The carbon matrix in the composite material is divided into surface carbon and inner carbon, not only facilitates the electronic conduction, but also inhibits the aggregation of ZnFe2O4 nanoparticles, which largely accommodates the mechanical stresses caused by the volume change of ZnFe2O4 during charge/discharge process. ZnFe2O4/C could maintain their integrity and provide excellent properties. The obtained ZnFe2O4/C has a specific capacity of 2055 mA h g−1 at 1000 mA g−1 and a capacity retention of 54% with the current density increasing from 100 to 5000 mA g−1. The excellent performance is derived from the unique compound structure and this facile fabrication method also has good prospects in synthesizing other materials.

Activated clay of nest structure encapsulated sulfur cathodes for lithium–sulfur batteries

Activated clay (AC) with a nest-like structure and a large surface area was employed to support sulfur as the cathode for lithium–sulfur batteries. The special structure may have a similar effect to small filter screens for entrapping sulfur and restricting the diffusion of polysulfides during cycling. A high capacity of 959.6 mA h g−1 was achieved at a rate of 0.1 C in the first cycle for the AC/S composite with a sulfur content of 57 wt% and the reversible capacity remained high at up to 700.9 mA h g−1 even after 50 cycles.

Excellent oxygen evolution reaction of NiO with a layered nanosphere structure as the cathode of lithium–oxygen batteries

A layered nanosphere structured NiO catalyst was successfully synthesized by a simple and efficient hydrothermal method as a cathode material for lithium–oxygen (Li–O2) batteries. Cyclic voltammetry (CV), dual electrode voltammetry (DECV) and chronoamperometry (CA) by rotating ring-disk electrode (RRDE) were carried out to investigate the catalytic activity of this catalyst for the oxygen evolution reaction (OER). The results revealed that the layered nanosphere NiO exhibited excellent electrochemical performance, stability and a typical four-electron reaction as a cathode electrocatalyst for rechargeable nonaqueous Li–O2 batteries. The overpotential of the NiO is only up to 0.61 V. X-ray photoelectron spectroscopy (XPS) characterization shows that the Li2O2 and Li2CO3 formed during the discharge process and decomposed after charging. Moreover, the cut-off voltage of discharging is about 2.0 V in the NiO-based Li–O2 batteries, while the specific capacity is up to 3040 mA h g−1. There is no obvious performance decline of the battery after 50 cycles at a current density of 0.1 mA cm−2 with a superior limited specific capacity of 800 mA h g−1. Herein, the layered nanosphere structured NiO catalyst is considered a promising cathode electrocatalyst for Li–O2 batteries.

In situ synthesis of metal embedded nitrogen doped carbon nanotubes as an electrocatalyst for the oxygen reduction reaction with high activity and stability

In this work, a Co–N doped carbon nanotube (CNT) catalyst was fabricated via a simple pyrolysis approach and the effects of solvothermal processing on the catalytic activity of the as-prepared material were investigated in detail. The results show that after solvothermal processing (Co-NC) the catalyst has a more homogeneous anemone structure, a higher nitrogen content, a larger BET surface area and a higher degree of graphitization compared to the catalyst produced after non-solvothermal processing (Co-MA). The results of electrochemical tests indicate that Co-NC, compared to commercial 20% Pt/C and Co-MA, has an improved mass transfer process and sufficient active site exposure, which brings about superb oxygen reduction electrocatalytic activity, a higher reduction potential (−0.2 V vs. Ag/AgCl), a limiting diffusion current (5.44 mA cm−2) and excellent stability in 0.1 M KOH solution.