A two-phase kinetic model is proposed for the emulsion grafting copolymerization of styrene and acrylonitrile in the presence of polybutadiene seed latex particles. The experimental results observed by conducting the polymerizations at 50 °C are compared with those predicted by the proposed kinetic model and confirm that the model is valid for predicting the rate of this emulsion grafting copolymerization. In the model predictions, thermodynamic equilibrium equations proposed in our previous papers are used for calculating the monomer concentrations in poly(styrene-co-acrylonitrile) domains and continuous polybutadiene matrix in acrylonitrile–butadiene–styrene terpolymer particles as emulsion grafting copolymerization proceeds. In addition, it is shown that the model is also applicable to predict grafting efficiency, copolymer composition of free and grafted chains.

Rose flower-like NiFe2O4 composite, uniformly distributed on 3D Ni foam substrate, is successfully prepared via a facile, cost-effective hydrothermal growth process followed by sintering. The structure of the sample is tested by X-ray diffraction while the morphology is characterized by scanning electron microscopy and transmission electron microscopy. The flower-like NiFe2O4 materials are applied as potential anode for lithium-ion batteries (LIBs) which have the highest energy density and play enssential role for the electronic vehicles and sodium ion batteries (SIBs) which are candidates for replacing LIBs because of the abundant nature storage. Electrochemical results confirmed that the anode exhibits good cycling performance with a stable specific capacity and rate capability both in LIBs and SIBs. Furthermore, the cycling performance for LIBs is demonstrated to be 1126 mAh g−1 even after 100 cycles while the Na storage behavior of rose flower-like NiFe2O4 materials as an anode material for SIBs is essentially investigated. It exhibits a high original discharge capacity of 584 mAh g−1, and steady capacity retention of 304 mAh g−1 after 100 cycles. Moreover, the long cycle capacity expressed to be ~250 mAh g−1 even after 1300 cycles suggests a good cycling performance in this report for SIBs.

•SE is an effective electrolyte additive for high temperature application of LiNi0.5Mn1.5O4.•A protective film can be formed on LiNi0.5Mn1.5O4 due to preferential oxidation of SE.•The film can suppress the dissolution of transition metal ions from LiNi0.5Mn1.5O4.Electrolyte additives are necessary for the application of high potential cathode in high energy density lithium ion batteries, especially at elevated temperature. However, the electrolyte additives that can effectively suppress the dissolution of transition metal ions from cathode have seldom been developed up to date. In this work, we propose a novel electrolyte additive, trimethylsilylcyclopentadiene (SE), for high temperature application of a representative high potential cathode, lithium nickel manganese oxide (LiNi0.5Mn1.5O4). It is found that the dissolution of Mn and Ni from LiNi0.5Mn1.5O4 can be effectively suppressed by applying SE. With applying 0.25% SE, the dissolved amount of Mn and Ni is decreased by 97.4% and 98%, respectively, after 100 cycles at 55 °C. Correspondingly, the cyclic performance of LiNi0.5Mn1.5O4 is significantly improved. Physical characterizations and electrochemical measurements show that SE can be preferentially oxidized and generate a protective film on LiNi0.5Mn1.5O4. The resulting film inhibits the electrolyte decomposition and the transition metal ion dissolution.

•Cyclability of LiCoO2/graphite full cell is improved notably by using TFTPN.•TFTPN is more easily oxidized on cathode or reduced on anode than electrolyte.•Protective interphase films formed simultaneously on cathode and anode by TFTPN.A novel electrolyte additive, tetrafluoroterephthalonitrile (TFTPN), is proposed to improve the cyclic stability of lithium cobalt oxide (LiCoO2)/graphite lithium-ion full cells up to 4.4 V. Electrochemical measurements indicate that TFTPN can be reduced on graphite electrode and oxidized on LiCoO2 electrode preferentially compared to the baseline electrolyte, 1.0 M LiPF6 in EC/DEC/EMC (1/1/1, in weight), and thus improves the cyclic stability of graphite/Li and LiCoO2/Li half cells, respectively. Further charge/discharge tests demonstrate that the cyclic stability of LiCoO2/graphite full cell can be significantly improved by TFTPN. A high capacity retention of 91% is achieved for the full cell using 0.5% TFTPN-containing electrolyte after cycling at 0.5C between 3.0 and 4.4 V for 300 cycles, compared to the 79% for that using the baseline electrolyte. This effect is attributed to the simultaneously formed protective interphase films on graphite and LiCoO2 by TFTPN due to its preferential reduction or oxidation. The resulting interphase films are verified by physical characterizations and theoretical calculations.Download high-res image (204KB)Download full-size image

Carbon-coated core-shell structure artificial graphite@plasma nano-silicon@carbon (AG@PNSi@C) composite, applying as lithium ion battery anode material, has been prepared via spray drying method. The plasma nano-silicon (<100 nm), which contained amorphous silicon, was synthesized by radio frequency induction plasma system with the high temperatures processing capability and high quench rates. The artificial graphite in the composite acts as the core which supports the particle and provides electroconductivity, while PNSi attached on the surface of the core, enhances the specific capacity of the composite. The as prepared composite shows superior performance as anode in lithium-ion batteries, regarding to the initial Coulombic efficiency and cycle life. The initial Coulombic efficiency of AG@PNSi@C electrode is 81.0% with a discharge capacity of 553 mAh g−1 and a recharge capacity of 448 mAh g−1. During cycling, AG@PNSi@C exhibits excellent performance with a very low capacity fading that the discharge capacity maintains 498.2 mAh g−1 and 449.4 mAh g−1 after 250 cycles and 500 cycles. AG@PNSi@C also shows enhanced resistance against high current density. Besides the remarkable electrochemical performances, the facile and mass-producible synthesis process makes the AG@PNSi@C composite very promising for its application in lithium-ion batteries.

Lithium manganese oxide (LiMn2O4) is one of the most promising cathodes for lithium ion batteries because of its abundant resources and easy preparation. However, its poor cyclability, especially under elevated temperature, limits its application on a large scale. In this work, it is reported that the cyclability of LiMn2O4 can be significantly improved by applying 4-(trifluoromethyl)benzonitrile (4-TB) as an electrolyte additive. Charge/discharge tests indicate that the capacity retention of LiMn2O4 after 450 cycles at 1C and 55 °C in a standard electrolyte, 1 M LiPF6 in EC/EMC/DEC (3 : 5 : 2, in weight), is improved from 19% to 69%. Further electrochemical and physical characterization demonstrates that 4-TB can, on the one hand, be electrochemically oxidized preferentially compared to the standard electrolyte, which generates a protective interphase film on LiMn2O4. On the other hand, 4-TB can effectively combine with protonic impurities, which inhibits the thermal decomposition of the electrolyte. This dual-functionality of 4-TB contributes to the significantly improved cyclability of LiMn2O4.

Several methods consisting of two or multi-step processes have been so far proposed for the preparation of sub- and micrometer-sized hollow polymer particles. In this study, we proposed an innovative one-step synthesis of the hollow polymer particles by applying microsuspension copolymerization of styrene and methyl acrylate with Mg(OH)2 as dispersant. In this method, Mg(OH)2 acted not only as dispersant, which covered densely at the surface of the monomer droplets, but also caused hydrolysis reaction of MA unit within styrene-methyl acrylate copolymer particles during the polymerization due to giving alkaline pH in the aqueous medium. It is also important that methyl acrylates are predominantly polymerized over styrene at the initial stage of the microsuspension copolymerization.

Novel self-assembled natural graphite composites (SANGs) were prepared by the granulation of natural graphite and styrene/acrylonitrile copolymer (SAN) particles by a spray-drying and subsequent pyrolysis procedure. In this work, monodispersed SAN particles with high residual carbon contents were prepared by the dispersion polymerization of acrylonitrile and styrene using the mixture initiators of 2,2′-azobis(isobutyronitrile) and benzoyl peroxide in the presence of polyvinylpyrrolidone in ethanol. The morphology and structure of SAN particles and SANGs were characterized by scanning electron microscopy (SEM), high resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD) and Raman spectroscopy. The residual carbon contents and the pyrolytic carbon composition of SAN particles were characterized by thermogravimetric analysis (TGA) and X-ray photoelectron spectroscopy (XPS). The as-prepared SANGs present more improved kinetic properties than those of natural graphite when used as anodes in Li-ion batteries. It is due to the self-assembled morphology of SANGs, which improves the less anisotropic transport of Li ions and facilitates the electrochemical kinetics during cycling.

This paper reports a series of novel Ni-based metal–organic framework (Ni–MOFs) prepared by a facile solvothermal process. The synthetic conditions have great effects on the Ni–MOFs morphologies, porous textures, and their electrochemical performance. Improved capacitance performance was successfully realized by the in-situ hybrid of Ni–MOFs with graphene oxide (GO) nanosheets (Ni–MOFs@GO). The pseudocapacitance of ca. 1457.7 F/g for Ni–MOFs obtained at 180 °C with HCl as the modulator was elevated to ca. 2192.4 F/g at a current density of 1 A/g for the Ni–MOFs@GO with GO contents of 3 wt %. Additionally, the capacitance retention was also promoted from ca. 83.5% to 85.1% of its original capacitance at 10 A/g even after 3000 cycles accordingly. These outstanding electrochemical properties of Ni-based MOF materials may be related to their inherent characteristics, such as the unique flower-like architecture and fascinating synergetic effect between the Ni–MOFs and the GO nanosheets.Keywords: graphite oxide; metal−organic framework (MOFs); nanocomposites; nickel; pseudocapacitor

A UiO-66-type metal–organic framework (MOF) fabricated with titanium was successfully prepared via a facial modified post-grafting method. The as-prepared samples were characterized by X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), ultraviolet-visible adsorption spectroscopy (UV-vis), and photoluminescence spectroscopy (PL) techniques. The introduction of titanium enhanced the optical properties of UiO-66 via the formation of oxo-bridged hetero-Zr–Ti clusters, but led to a sacrifice in crystallinity. The removal of methylene blue (MB) over these samples could be attributed to the dual function of the adsorption and photo-degradation mechanisms. The highest MB removal efficiency of 87.1% was achieved over UiO-66(1.25Ti) under simulated sun-light irradiation.

Using a simple hydrothermal procedure, cobalt oxide (Co3O4) with preferred orientation along (220) planes is in situ prepared and coated on MWCNT. The prepared Co3O4@MWCNT nanocable shows superior electrochemical performance as cathode material for aqueous supercapacitors in 0.5 M KOH solution. Its redox peaks retain the well-defined shapes even when the scan rate increases to 200 mV/s. Its specific capacitance is high, 590 F/g at 15 A/g and 510 F/g even at 100 A/g within the potential range from −0.2 to 0.58 V (vs SCE). There is no capacitance fading after 2000 full cycles. This excellent performance is superior to the pristine and the reported Co3O4, which is ascribed to the unique nanocable structure with orientation.Keywords: cathode; Co3O4@MWCNT; nanocable; rate performance; supercapacitor

•The materials was prepared by a simple high-energy wet ball milling method.•The method is environmentally friendly, high yield and low-cost, thus, suitable for large scale industrial production.•The final product shows excellent electrochemical properties.A high yield and low-cost high-energy wet ball milling method is used for producing nano-flake Si@SiO2 as an anode material for Li-ion batteries. After a two-step ball milling (coarse milling and fine milling) process, the irregular plate-like micrometric Si (average particle size is 27.4 μm) is fractured into nano-flake Si@SiO2 (average particle size is 154.8 nm) with small crystalline grains and abundant grain boundaries. Due to the significant changes of the prepared nano-flake Si@SiO2 in the surface composition, particle size and crystal structure, the ball milled Si shows better electrochemical performance compared with the as-received micrometric Si. And the fine milled Si shows the best electrochemical properties with a high initial coulombic efficiency of 84.6% and a specific capacity of 1920.4 mA h g−1 at a current density of 100 mA g−1 after 100 cycles.

Titanium species were immobilized on α-ZrP nanosheets (ZrP–Ti) using a modified post-grafting method. The obtained ZrP–Ti composites were characterized via Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), ultraviolet-visible (UV-vis) absorption spectroscopy, photoluminescence spectroscopy (PL), and scanning electron microscopy (SEM). Titanium species in the form of TiO2−x clusters with an average particle size of 2–5 nm were grafted on α-ZrP nanosheets via chemical bonding with P element. These ZrP–Ti composites could be well dispersed in polar solvents to ensure that the TiO2−x clusters bonded on both faces of the nanosheets were accessible. The ZrP–Ti composites presented enhanced visible-light absorption properties compared with that of pure TiO2. These features allowed them to exhibit better photocatalytic activities for the photodegradation of methylene blue (MB) under solar irradiation. The TiO2−x clusters tended to aggregate into anatase phase TiO2 when the molar ratio of P/Ti exceeded 1:1, and this reversed the advantage in their photocatalytic activities. The best MB degradation efficiency of 100% with the apparent rate constant of 0.054 min−1 was achieved over the ZrP–Ti composite with the P/Ti molar ratio of 1:1.

The green emission accompanied with intense red phosphorescence is observed from the tris(8-hydroxyquinoline) aluminum (Alq3) in the heavily doped tris(2-phenylpyridine) iridium [Ir(ppy)3] films. This photoluminescence (PL) emission mechanism is studied by the PL excitation (PLE) spectra for the red and green emissions. From the PLE spectrum for the red emission, the energy transfer from Ir(ppy)3 to Alq3 is confirmed. The increase of the green emission with increasing temperature from 12 K is explained by the endothermic back Förster energy transfer from the triplet T1 state of Ir(ppy)3 to the singlet S1 state of Alq3. It is suggested that this back transfer is partially responsible for the decrease of the red emission intensity corresponding to the increase of the green emission. Unlike the Förster energy transfer, the Dexter energy transfer from the T1 state of Ir(ppy)3 to the T1 state of Alq3 is highly efficient. The explanation for this process is presented here. The green emission is not attributed to Ir(ppy)3 but to Alq3, because not only the green emission profile but also the red emission profile is quite similar to the δ-phase polycrystalline Alq3. From these results, it is concluded that the Alq3 forms a δ-phase polycrystalline state to accept the phosphor sensitization. The unusual enhancement of the red phosphorescence from the Alq3 is explained by the mixing of the T1 state of Ir(ppy)3 with the T1 state of Alq3 under the Dexter energy transfer of short range process, by taking into account that the T1 state of Ir(ppy)3 contains the singlet state by the strong spin–orbit coupling.

Novel self-assembled natural graphite composites (SANGs) were prepared by the granulation of natural graphite and styrene/acrylonitrile copolymer (SAN) particles by a spray-drying and subsequent pyrolysis procedure. In this work, monodispersed SAN particles with high residual carbon contents were prepared by the dispersion polymerization of acrylonitrile and styrene using the mixture initiators of 2,2′-azobis(isobutyronitrile) and benzoyl peroxide in the presence of polyvinylpyrrolidone in ethanol. The morphology and structure of SAN particles and SANGs were characterized by scanning electron microscopy (SEM), high resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD) and Raman spectroscopy. The residual carbon contents and the pyrolytic carbon composition of SAN particles were characterized by thermogravimetric analysis (TGA) and X-ray photoelectron spectroscopy (XPS). The as-prepared SANGs present more improved kinetic properties than those of natural graphite when used as anodes in Li-ion batteries. It is due to the self-assembled morphology of SANGs, which improves the less anisotropic transport of Li ions and facilitates the electrochemical kinetics during cycling.