Hongyun Yue

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)).

First-principles and experimental study of nitrogen/sulfur co-doped carbon nanosheets as anodes for rechargeable sodium ion batteries

Heteroatom doped carbon materials have recently demonstrated an outstanding sodium storage ability and are being considered as the most promising candidate as anodes for sodium ion batteries. However, there is limited understanding of the relationship between structural and electronic properties and electrochemical storage capacity. First-principles calculations on a doped graphene cluster propose that N, S co-doping can promote the electronegativity, adsorption capacity of Na atoms and diffusion of Na+ ions on graphene sheets, especially for the sample consisting of more pyridinic-N, while excessive O atoms may alleviate these. All these features render N, S co-doped carbon as a superior anode for sodium ion batteries. Therefore, the N, S co-doped carbon nanosheets are fabricated via a simple thermal treatment method using gelatin as the carbon source and thiourea as the N and S precursor. The optimized product (mgelatin : mthiourea = 1 : 10) results in a superb cycling capacity of 300 mA h g−1 after 500 cycles, with a coulombic efficiency of ∼100%. This study provides a facile and reliable route to prepare co-doped carbon with enhanced sodium storage properties.

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.

In situ preparation of cobalt doped ZnO@C/CNT composites by the pyrolysis of a cobalt doped MOF for high performance lithium ion batteries

Co doped ZnO embedded in carbon/carbon nanotube composites (CZO@C/CNT) was prepared in situ during the calcination of Co-MOF-105 at 600 °C. A lower crystallinity demonstrated weaker binding force in Co-MOF-105, which made it possible for Co ions to break away from the crystal and reduce to metal Co during the pyrolysis process. The formation of CNTs was catalyzed by Co metal and the carbon source was terephthalic acid, which acted as the organic linker in the MOF. Moreover, the sp2 hybridization of the carbon atoms in terephthalic acid decreased the energy barrier during the growth of CNTs. From TEM and SEM observation, the CNTs were interspersed in the material and connected the CZO@C nanoparticles together, which made the electron transfer easier. The other advantages of Co doping were enhancing the conductivity of ZnO and increasing the graphitization degree of the carbon on the surface of the CZO@C nanoparticles. When the CZO@C/CNT composite was used as an anode material for lithium ion batteries, an enhanced electrochemical performance of 758 mA h g−1 after 100 cycles at a current density of 100 mA g−1 was obtained.

Bio-inspired synthesis of ordered N/P dual-doped porous carbon and its use as anode for sodium-ion batteries.

Carbonaceous materials are one of the most promising anode materials for sodium-ion batteries, because of their abundance, stability, and safe usage. However, the practical application of carbon materials is hindered by poor specific capacity and low initial Coulombic efficiency. The design of porous structure and doping with heteroatoms are two simple and effective methods to promote the sodium storage performance. Herein, the N, P co-doped porous carbon materials are fabricated using renewable and biodegradable gelatin as carbon and nitrogen resource, phosphoric acid as phosphorus precursor and polystyrene nanospheres as a template. The product can deliver a reversible capacity of 230 mA h g-1 at a current density of 0.2 A g-1 , and even a high capacity of 113 mA h g-1 at 10 Ag-1 . The enhanced sodium storage performance is attributed to the synergistic effect of the porosity and the dual-doping of nitrogen and phosphorus.

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.

A novel modified PP separator by grafting PAN for high-performance lithium–sulfur batteries

A novel modified separator was synthesized with an ultraviolet irradiated polypropylene (PP) membrane and acrylonitrile monomers by a solution grafting reaction. It was demonstrated that polyacrylonitrile (PAN) was grafted on the PP separator surface by analyzing the results of FESEM, ATR–FTIR and XPS. The thermostability and wettability of the PAN-grafted PP (PP-g-PAN) separator were enhanced. Then, Li–S batteries were assembled using the modified separators. The cycling and rate capacity performance is improved clearly because of the higher liquid uptake, smaller porous size, better polysulfides absorption effect and interfacial affinity of the grafted separator. The modified separator can hinder the movement of Li2Sx effectively to prevent the shuttle effect of a Li–S battery. Therefore, this efficient method has great potential to be applied to the modification of other kinds of polymer membranes.

Sulfur grown around carbon nanotubes as a cathode material for Li/S battery

Sulfur/multi-walled carbon nanotubes (MWCNTs) composites have been successfully prepared by an in situ growth strategy as a cathode material for lithium/sulfur battery. The microstructure and morphology of the sulfur/MWCNTs composites are characterized by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). From the results, it is found that the nano-sulfur (shell) grows around the MWCNTs (core) and is well-dispersed over the whole surface of the MWCNTs. Tested by coin type cells, the composite materials exhibited the sulfur utilization approaching to 78% for the first cycle, the capacity retention closing to 84% after 100 cycles at various rates. The excellent electrochemical performance could be attributed to the nano-size sulfur and the homogeneous distribution of sulfur on MWCNTs matrix, resulting from this novel in situ growth method, which not only enhances the reactive activity of sulfur during charge–discharge processes but also provides stable electrical and ionic transfer channels.

Biomimetic Synthesis of Polydopamine Coated ZnFe2O4 Composites as Anode Materials for Lithium-Ion Batteries

Metal oxides as anode materials for lithium storage suffer from poor cycling stability due to their conversion mechanisms. Here, we report an efficient biomimetic method to fabricate a conformal coating of conductive polymer on ZnFe2O4 nanoparticles, which shows outstanding electrochemical performance as anode material for lithium storage. Polydopamine (PDA) film, a bionic ionic permeable film, was successfully coated on the surfaces of ZnFe2O4 particles by the self-polymerization of dopamine in the presence of an alkaline buffer solution. The thickness of PDA coating layer was tunable by controlling the reaction time, and the obtained ZnFe2O4/PDA sample with 8 nm coating layer exhibited an outstanding electrochemical performance in terms of cycling stability and rate capability. ZnFe2O4/PDA composites delivered an initial discharge capacity of 2079 mAh g–1 at 1 A g–1 and showed a minimum capacity decay after 150 cycles. Importantly, the coating layer improved the rate capability of composites compared to that of its counterpart, the bare ZnFe2O4 particle materials. The outstanding electrochemical performance was because of the buffering and protective effects of the PDA coating layer, which could be a general protection strategy for electrode materials in lithium-ion batteries.