Qiuxian Wang

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)).

Submicron peanut-like MnCO3 as an anode material for lithium ion batteries

Submicron peanut-like MnCO3 is prepared by a facile homogeneous precipitation and delivers better electrochemical performance as an anode material for lithium ion battery. The physical characterization reveals that the peanut-like MnCO3 is composed of irregular nanoparticles, which results in a large surface area. As a contrast, square MnCO3 is obtained with structural directing agents. Submicron peanut-like MnCO3 delivers a reversible specific capacity of 700 mA h g−1 at 233 mA g−1 (1C = 466 mA g−1) after 140 cycles. The discharge capacities at 46, 93, 233, 466, 932, and 2330 mA g−1 are 1047, 1038, 881, 843, 750 and 410 mA h g−1, respectively, and a recovery capacity of 1100 mA h g−1 after 60 cycles could still be obtained. It also displays a discharge capacity of 618 mA h g−1 at high current density of 932 mA g−1 after 80 cycles. The advanced performance can be attributed to the unique morphology, facile electron and Li+ transportation at the electrode/electrolyte interface and self-accommodation of the large volume change during discharge/charge.

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.

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.

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.

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.

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.