Nano-scale silicon particles were successfully decorated uniformly on a LiFePO4@C electrode through utilization of spray technique. The electrochemical measured results indicate that the Si surface modification results in improved electrochemical performances for commercial 18 650 cylindrical batteries, especially at elevated temperature, which is attributed to the fact that Si introduction can enable the LiFePO4 electrodes to suppress cylindrical battery degradation. Based on the analysis of structural characterization, it is revealed that the battery cathode with Si modification retains a better LiFePO4 phase and exhibits less Li+ loss. In addition, the negative electrode of the battery contains a better graphite carbon structure and a thinner thickness of SEI film due to Si decoration. Furthermore, the related high-temperature aging and degradation mechanisms of the batteries were discussed.

•Nanostructured composites of V2O5/Cu have been prepared for LIBs.•The V2O5/Cu electrodes exhibit good performance for lithium batteriess.•The enhanced performance is ascribed to the nanosized V2O5 and conductive Cu NPs.In order to overcome the intrinsic drawbacks of V2O5, including the intrinsically low electrical conductivity and slow electrochemical kinetics, V2O5 nanospheres are uniformly mixed with the electric Cu nanoparticles for forming V2O5/Cu composites. As used as an cathode material for LIBs, the V2O5/Cu composite demonstrated obviously improved electrochemical performance including high reversible specific capacity, superior rate capability and outstanding cycling stability. The V2O5/Cu cathodes can afford a high reversible capacity of 186 mAh g−1 after 70 cycles under a current density of 300 mA g−1 and good rate performance. Even at a high current density of 5 A g−1, a high reversible capacity of 101 mAh g−1 after 350 cycles can still remain. The improved performance can be contributed from the decorated Cu nanoparticles, which can result in a good contact in active materials and facilitate transportation of the electron into the inner region of the electrode.Download high-res image (134KB)Download full-size image

•The interfaces with O–Ni combining bonds are more energetically favorable.•The change of EWF is 1.8 eV for Hf terminated interfaces with Ni substitution for Hf.•The change of EWF is 3.2 eV for Hf terminated interfaces with Hf vacancy.•The change of EWF is 2.0 eV for O terminated interfaces with O vacancy.•Results are explained by interface dipole density, ionic valence and occupied states.The effective work functions and formation energies for Ni/HfO2 interfaces with and without defects, including interfacial intrinsic atom substitution and atom vacancy in interfacial layer were studied by first-principles methods based on density functional theory (DFT). The calculated results of the formation energies indicate that the interfaces with O–Ni combining bonds in the interfacial region are more energetically favorable and a small amount O vacancy is comparatively easy to form in O–Ni interface, especially under O-rich situation. Moreover, the results of our calculations also reveal that, (1) the effective work functions strongly depend on the type of interface, interface roughness and atom substitution content in the interface region; (2) for Hf–Ni interfaces, two calculated effective work functions without and with Ni substitutions in whole interfacial Hf layer are good for nMOS and pMOS effective work function (EWF) engineering, respectively; (3) the EWFs are sensitive to Hf vacancy rather than Ni vacancy in interfacial layer for Hf–Ni interfaces; (4) oxygen vacancies can result in a decrease of effective work function for O–Ni interfaces. Additionally, we establish an expected theoretical relationship that variations of the EWFs are in proportion to that of interface dipole density. Finally, ionic valence state and occupied state are used to qualitatively analyze and explain the effects of interfacial defects on the EWF in metal-oxide interfaces. Our work suggests that controlling interfacial intrinsic atom substitution and interface roughness are attractive and promising ways for modulating the effective work function of Ni/HfO2 interfaces.

•LiFePO4@C/Si possesses faster charged and discharged velocity than LiFePO4@C.•Si surface modification promotes Li+ ion transfer rate.•Si surface modification suppresses the Fe dissolution and enhances the stability of LiFePO4 and cycle performance.In this letter, Li+ ion kinetic processes of LiFePO4@C and LiFePO4@C modified by nano silicon (LiFePO4@C/Si) have been systematically investigated by X-ray diffraction, Raman spectra and Electrochemical impedance spectroscopy (EIS), respectively. The experimental results indicate that, (1) LiFePO4@C/Si possesses faster charged and discharged velocity than LiFePO4@C; (2) the nano silicon surface modification induces the larger diffusion coefficient and less activation energy of Li ions, which promotes Li+ ion transfer rate; (3) it suppresses effectively the Fe dissolution and enhances the stability of LiFePO4 phase and cycle performance; (4) there exists the best silicon surface modification content (Si content = 2.46 at.%) in enhancing the electrochemical performances of LiFePO4. Additionally, it is suggested that constant-voltage charge is with some time indispensable for a fully delithiation of the LiFePO4 material.

In this paper, homogeneous composites of pomegranate-structured SnO2@C/Cu have been prepared by a simple hydrothermal reaction coupled with wet-chemical reduction, and directly used as anode materials for lithium ion batteries (LIBs). These SnO2@C/Cu anodes with an unique architecture show good LIB performance with a capacity of 660 mAh g−1 tested at 600 mA g−1 after 50 cycles and good rate performance at room temperature. Compared with the pure SnO2 and SnO2@C, SnO2@C/Cu anodes exhibit much better low-temperature electrochemical performance including reversible capacity, cycling performance, and rate performance. The good LIB performance of SnO2@C/Cu anodes should be associated with carbon shell and the conducting Cu particles. This unique configuration can prevent the agglomeration of active materials and facilitate electron conduction especially at a relative low temperature, and obtain the capacity stability in cycling process for LIBs.

•NiCo2O4 nanosheets with different microstructures were controllably synthesized.•Ultrathin NiCo2O4 nanosheets possess a mesoporous structure and large surface area.•Ultrathin NiCo2O4 nanosheets exhibit a high reversible capacity of 690.4 mA h g−1.Two kinds of the NiCo2O4 nanosheets constructed by interconnected nanoparticles with different microstructures, including ultrathin NiCo2O4 nanosheets (NiCo2O4-UNSs) and common NiCo2O4 nanosheets (NiCo2O4-NSs), were controllably synthesized by a facile method. The structure and morphology of the NiCo2O4 nanosheets were analyzed and characterized by XRD, SEM and TEM. NiCo2O4-UNSs possess a large surface area (119 m2 g−1) and narrow pore distribution (around 5 nm). Subsequently, the Na-ion storage properties of such NiCo2O4 nanosheets were investigated by sodium half-cells. The ultrathin NiCo2O4 nanosheets (NiCo2O4-NSs) exhibit much improved performance than that of NiCo2O4-NSs with a high reversible capacity of 690.4 mA h g−1 at 100 mAg−1 and 141.8 mA h g−1 at the current density of 1000 mA g−1 in the voltage window of 0.01–2.5 V. Furthermore, a reversible capacity of about 203.7 mA h g−1 can be remained after 50 cycles at 200 mAg−1.

•β-FeOOH/MWNT catalysts for lithium–O2 batteries have been synthesized by a wet chemical method.•The obtained electrodes exhibit high specific capacity, good rate capability and cycle stability.•The enhanced performance is ascribed to the synergetic effects between MWNTs and β-FeOOH.A novel composite of β-FeOOH nanospindles coated on multi-walled carbon nanotubes (β-FeOOH/MWNTs) has been synthesized via a wet chemical method and used as electrocatalysts for the cathodes of Li–O2 batteries (LOBs). The β-FeOOH/MWNT cathodes can afford a high reversible capacity of 6000 mA h g−1 tested at 200 mA g−1 and cycle stability for 19 cycles with a reversible capacity of 600 mA h g−1 and good rate capability. The LOB performance should be benefited from the fast kinetics of electron transport through the MWNT support and the electro-catalytic activity provided by the β-FeOOH nanospindles. The preliminary result manifests that the composites of β-FeOOH/MWNTs are promising cathode electrocatalysts for LOBs.Composites of β-FeOOH/MWNT are synthesized and used as high performance catalysts for lithium–O2 batteries.

•N doping on the LiFePO4 (010) surface is energetically favored.•A much smaller band gap of the N-doped LiFePO4 (010) surface is predicted.•High intrinsic energy barrier of Li surface diffusion retards fast Li transport.•N doping reduces the Li-ion diffusion activation energies at the surface.•The N surface-modified LiFePO4 exhibits higher electronic and ionic conductivity.The structural, electronic and Li-ion diffusion properties of N-doped LiFePO4 (010) surface have been investigated by first-principles calculation under the DFT + U framework. The calculated results show that the substitution of nitrogen for oxygen on the (010) surface of the LiFePO4 is energetically favored and N-substitution can significantly decrease the band gap of the LiFePO4, indicating better electronic conductive properties. The nudged elastic band (NEB) method is used to calculate the activation energy for Li-ion diffusion. It is found that for pure LiFePO4 (010) surface high intrinsic activation energy of Li-ion diffusion retards fast Li transport. However, this energy barrier can be effectively reduced by nitrogen surface modification. Our results imply that N doping on the LiFePO4 (010) surface could improve its electron conductivity and ion diffusion properties.

Designing an efficient catalyst is essential to improve the electrochemical performance for Li–O2 batteries. In this study, the novel composites of Fe/Fe3C carbon nanofibers (Fe/Fe3C–CNFs) were synthesized via a facile electrospinning method and used as cathode catalysts for Li–O2 batteries. Owing to their favorable structures and desirable bifunctional catalytic activities, the resulting cathodes with a Fe/Fe3C–CNF catalyst exhibited superior electrochemical performance with high specific capacity, good rate capability and cycle stability. It is revealed that the synergistic effect of the fast kinetics of electron transport provided by the CNF support and the high electro-catalytic activity provided by the Fe/Fe3C composites resulted in the excellent performance for Li–O2 batteries. The preliminary result manifests that the composites of Fe/Fe3C–CNFs are promising cathode electrocatalysts for Li–O2 batteries.

Ternary spinel MFe2O4 (M = Co, Ni) nanoparticles coated on multi-walled carbon nanotubes (MFe2O4/CNTs) were prepared via a simple hydrothermal method. Owing to their favorable structures and desirable bi-functional oxygen reduction and evolution activities, the resulting MFe2O4/CNT (M = Co, Ni) composites as electrocatalysts for the cathodes deliver better electrochemical performance during the discharge and charge processes compared with that of the pure carbon of ketjen black (KB). The good performance can be attributed to the excellent catalytic activity of highly dispersed MFe2O4 (M = Co, Ni) nanoparticles and facile electron transport by supporting CNTs. This preliminary result manifests that the ternary spinel MFe2O4/CNT (M = Co, Ni) composites are promising cathode electrocatalysts for non-aqueous Li–O2 batteries.

Designing an effective microstructural cathode combined with a highly efficient catalyst is essential for improving the electrochemical performance of Li-O2 batteries (LOBs), especially for long-term cycling. We present a nickel foam-supported composite of Pt nanoparticles (NPs) coated on self-standing carbon nanotubes (CNTs) as a binder-free cathode for LOBs. The assembled LOBs can afford excellent electrochemical performance with a reversible capacity of 4050 mAh/g tested at 20 mA/g and superior cyclability for 80 cycles with a limited capacity of 1500 mAh/g achieved at a high current density of 400 mA/g. The capacity corresponds to a high energy density of ∼3000 Wh/kg. The improved performance should be attributed to the excellent catalytic activity of highly dispersed Pt NPs, facile electron transport via loose CNTs connected to the nickel foam current collector, and fast O2 diffusion through the porous Pt/CNTs networks. In addition, some new insights from impedance analysis have been proposed to explain the enhanced mechanism of LOBs.Keywords: electrochemical performance; Li-O2 batteries; Pt/CNTs-NF cathodes; synergistic effect

•YBa2Cu3O7-coating enhances the rate capability and cyclability of LiNi0.5Mn1.5O4.•Superconducting YBa2Cu3O7 reduces charge-transfer resistance in a wide temperature.•YBa2Cu3O7 facilitates the kinetics for lithium diffusion at low temperature.LiNi0.5Mn1.5O4 modified with superconducting YBa2Cu3O7 (YBCO) is synthesized by mixing as-prepared LiNi0.5Mn1.5O4 powders and the sol–gel-driven YBa2Cu3O7 matrix, subsequently followed by high-temperature calcinations. The effect of YBCO-modification on the electrochemical performances of LiNi0.5Mn1.5O4@YBCO cells in a wide operation temperature is investigated systematically by the charge/discharge testing, cyclic voltammograms and AC impedance spectroscopy, respectively. In comparison with the pristine LiNi0.5Mn1.5O4, LiNi0.5Mn1.5O4@YBCO samples exhibit higher capacity, better cyclability and higher rate capability in a wide operation temperature range. An analysis of the electrochemical measurements reveals that the improved performance of LiNi0.5Mn1.5O4@YBCO is due to the better electric contact among particles, much lower charge-transfer resistances and higher lithium diffusion rate, especially at low temperature. In addition, the homogeneous YBCO layer formed on the LiNi0.5Mn1.5O4 protects the active materials from chemical attack by HF, which suppresses the dissolution of Ni or Mn from LiNi0.5Mn1.5O4 in the LiPF6 based electrolyte.

The structural stability, vibrational and magnetic properties of hydrogen doped ZnO:Co have been studied by first-principles calculations based on density functional theory. Bond-center (BC) sites were identified to be most stable sites for hydrogen, the corresponding vibrational frequencies including anharmonic contributions were calculated. Its magnetic properties were investigated as well. The calculated results reveal that hydrogen could induce the change of electronic transfer, leading to a decrease of magnetic moment. However, the magnetic coupling between Co atoms is greatly strengthen. The results simulated by Monte Carlo method indicate that hydrogen can induce the Curie temperature to increase from 200 to 300 K.

The surface of LiFePO4/C cathode material is coated with nano-sized Sn via a simple electroless deposition (ED) process, and the effects of the Sn-coating on the electrochemical performances of LiFePO4/C are investigated systematically by the charge/discharge testing, cyclic voltammograms and AC impedance spectroscopy, respectively. In comparison with the pristine LiFePO4/C, the Sn-coated LiFePO4/C exhibits higher capacity, better cyclability and higher rate capability in a wide operation temperature range. An analysis of the electrochemical measurements reveals that Sn-coated LiFePO4/C has good electric contact among particles, much lower charge-transfer resistances and higher lithium diffusion rate, especially at low temperature. In addition, the Sn-coating layer protects the active materials from chemical attack by HF and thus suppresses the dissolution of Fe from LiFePO4 in the LiPF6 based electrolyte.Highlights► With Sn-coating, the electrochemical performance of LiFePO4 is improved in a wide operation temperature. ► Metallic Sn layer suppresses the Fe dissolution and reduce the charge-transfer resistance. ► High conductive Sn facilitates the kinetics for lithium diffusion at low temperature.

Coaxial MWNTs@MnO2 confined in conducting polypyrrole (PPy) has been synthesized through an in situ polymerization of pyrrole monomers in the presence of prepared MWNTs@MnO2. As an anode in lithium batteries (LIBs), the obtained MWNTs@MnO2@PPy shows a high reversible capacity of 530 mA h g−1 tested at 1000 mA g−1 even after 300 cycles and an excellent rate performance. The superior electrochemical performance of the nanocable MWNTs@MnO2@PPy is associated with a synergistic effect of the MWNT matrix and the highly conducting PPy coating layer. This nanocable configuration not only facilitates electron conduction but also maintains the structural integrity of active materials. In addition, an analysis of the AC impedance spectroscopy and the corresponding hypothesis for DC impedance confirm that such configuration can effectively enhance the charge-transfer efficiency and the lithium diffusion coefficient. Thus, PPy modification supplied a promising route to obtain manganese oxide based anode in order to achieve high-performance LIBs.Composites of MWNTs@MnO2 coated by PPy are synthesized via a facile method to improve the electrochemical performance.

LiFePO4/Si composites are synthesized via a simple milling isopropanol mixtures process, and the effects of Si-modification on the electrochemical performances of LiFePO4 are investigated systematically by charge/discharge testing, cyclic voltammograms and AC impedance spectroscopy, respectively. In comparison with the pristine LiFePO4, LiFePO4/Si-nanoparticle shows better cyclability and higher rate capability, especially at elevated temperature. An analysis of the electrochemical measurements indicates that Si incorporation could significantly improve the electrochemical performance at high charge/discharge rate and elevated temperature. Among the investigated samples, (LiFePO4)98/(Si)2 sample shows the best electrochemical performance with 150 mAhg−1 at 0.5C at 60 °C. The enhancement could be mainly attributed to the lower charge-transfer resistance and higher lithium diffusion coefficients. In addition, the dangling bonds of Si and fluorosilica compounds are responsible for suppressing the dissolution of Fe2+ from olivine phase and preventing the rise of the surface resistance and charge transfer resistance.Highlights► LiFePO4/Si shows superior C-rate and elevated-temperature performances. ► H+ is suppressed by hydrogen bonding to the silicon dangling bonds in α-Si film. ► Fluorosilica on LiFePO4 hinders the interaction between LiFePO4 and electrolyte. ► Oxidized silicon injects electrons and generates a current during the dissolution.

In this paper, we investigate, by molecular dynamics simulations, the mechanical properties of a new carbon nanostructure, termed a graphene nanochain, constructed by sewing up pristine or twisted graphene nanoribbons (GNRs) and interlocking the obtained nanorings. The obtained tensile strength of defect-free nanochain is a little lower than that of pristine GNRs and the fracture point is earlier than that of the GNRs. The effects of length, width and twist angle of the constituent GNRs on the mechanical performance are analyzed. Furthermore, defect effect is investigated and in some high defect coverage cases, an interesting mechanical strengthening-like behavior is observed. This structure supports the concept of long-cable manufacturing and advanced material design can be achieved by integration of nanochain with other nanocomposites. The technology used to construct the nanochain is experimentally feasible, inspired by the recent demonstrations of atomically precise fabrications of GNRs with complex structures [Phys. Rev. Lett., 2009, 102, 205501; Nano Lett., 2010, 10, 4328; Nature, 2010, 466, 470].

MnO2 nanoflakes coated on carbon nanohorns (CNHs) has been synthesized via a facile solution method and evaluated as anode for lithium-ion batteries. By using CNHs as buffer carrier, MnO2/CNH composite displays an excellent capacity of 565 mA h/g measured at a high current density of 450 mA/g after 60 cylces.Keywords: buffer carrier; cycling performance; lithium-ion batteries; MnO2/CNH anode;

La0.7Sr0.3MnO3-coated 5 V spinel LiNi0.5Mn1.5O4 as cathode is prepared by mixing LiNi0.5Mn1.5O4 powders and the sol–gel-drived La0.7Sr0.3MnO3 matrix, followed by high-temperature calcinations. The effect of La0.7Sr0.3MnO3-coating on the electrochemical performances of LiNi0.5Mn1.5O4 cells, especially at elevated temperature, is investigated systematically by the charge/discharge testing, cyclic voltammograms and AC impedance spectroscopy, respectively. Compared to pristine LiNi0.5Mn1.5O4, La0.7Sr0.3MnO3-coated material has much lower surface and charge-transfer resistances and shows a higher lithium diffusion rate. The results of electrochemical experiments demonstrate that the modified material exhibits remarkably enhanced electrochemical reversibility and stability at elevated temperature. The La0.7Sr0.3MnO3-coating layer protected the surface of the active materials from HF in the electrolyte during electrochemical cycling. As a result, the electrochemical cycling stability is improved.Highlights► With La0.7Sr0.3MnO3-coating the rate performance and thermal storage of LiNi0.5Mn1.5O4 is improved. ► High conductive La0.7Sr0.3MnO3 is responsible for the improved performance at high-temperature. ► La0.7Sr0.3MnO3 layer suppresses the Mn dissolution and reduce the charge-transfer resistance.

The magnetism and work function of pure Ni(001) and Ni-Cu slab alloys were investigated using first-principles methods based on density functional theory. The calculated results reveal that both magnetic moments and work functions of the alloys depend strongly on the surface orientation, but hardly on the distribution of doped Cu atoms for a given surface orientation. It is found that the doped Cu atoms have evident influence on the magnetic moment of Ni-Cu slabs, and the average magnetic moment of Ni atoms for Ni-Cu alloys decreases with increasing concentration of Cu atoms. Moreover, it is observed that the work function of Ni(001) is insensitive to the supercell thickness and the inner concentration of Cu atoms. In the meantime, the spin polarization is found to have an obvious role on the work function of the Ni-Cu alloys, which may give a new way to modulate the work function of the metal gate.

Cr2O3-coated LiNi1/3Co1/3Mn1/3O2 cathode materials were synthesized by a novel method. The structure and electrochemical properties of prepared cathode materials were measured using X-ray diffraction (XRD), scanning electron microscopy (SEM), charge-discharge tests, cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS). The measured results indicate that surface coating with 1.0 wt% Cr2O3 does not affect the LiNi1/3Co1/3Mn1/3O2 crystal structure (α-NaFeO2) of the cathode material compared to the pristine material, the surfaces of LiNi1/3Co1/3Mn1/3O2 samples are covered with Cr2O3 well, and the LiNi1/3Co1/3Mn1/3O2 material coated with Cr2O3 has better electrochemical performance under a high cutoff voltage of 4.5 V. Moreover, at room temperature, the initial discharging capacity of LiNi1/3Co1/3Mn1/3O2 material coated with 1.0 wt.% Cr2O3 at 0.5C reaches 169 mAh·g−1 and the capacity retention is 83.1% after 30 cycles, while that of the bare LiNi1/3Co1/3Mn1/3O2 is only 160.8 mAh·g−1 and 72.5%. Finally, the coated samples are found to display the improved electrochemical performance, which is mainly attributed to the suppression of the charge-transfer resistance at the interface between the cathode and the electrolyte.

Olivine structured LiFePO4/C (lithium iron phosphate) and Mn2+-doped LiFe0.98Mn0.02PO4/C powders were synthesized by the solid-state reaction. The effects of manganese partial substitution and different carbon content coating on the surface of LiFePO4 were considered. The structures and electrochemical properties of the samples were measured by X-ray diffraction (XRD), cyclic voltammetry (CV), charge/discharge tests at different current densities, and electrochemical impedance spectroscopy (EIS). The electrochemical properties of LiFePO4 cathodes with x wt.% carbon coating (x= 3, 7, 11, 15) at γ =0.2C, 2C (1C= 170 mAh·g−1) between 2.5 and 4.3 V were investigated. The measured results mean that the LiFePO4 with 7 wt.% carbon coating shows the best rate performance. The discharge capacity of LiFe0.98Mn0.02PO4/C composite is found to be 165 mAh·g−1 at a discharge rate, γ = 0.2C, and 105 mAh·g−1 at γ =2C, respectively. After 10 cycles, the discharge capacity has rarely fallen, while that of the pristine LiFePO4/C cathode is 150 mAh·g−1 and 98 mAh·g−1 at γ=0.2 and 2C, respectively. Compared to the discharge capacities of both electrodes above, the evident improvement of the electrochemical performance is observed, which is ascribed to the enhancement of the electronic conductivity and diffusion kinetics by carbon coating and Mn2+-substitution.

Amorphous silicon (α-Si) films are deposited on LiFePO4@C electrode by using vacuum thermal evaporation deposition technique and the effect of α-Si film on electrochemical performance of LiFePO4@C cells is investigated systematically by the charge–discharge testing, cyclic voltammograms and AC impedance spectroscopy, respectively. The results reveal that the present of α-Si film on electrode surface could remarkably improve the electrochemical performance at high charge/discharge rate, especially at elevated temperature. This enhancement may be attributed to the amelioration of the electrochemical dynamics on the electrode/electrolyte interface resulting from the beneficial effects of α-Si film, which might significantly suppress the rise of both of the surface film resistance and charge transfer resistance.Highlights► The electrochemical performance at elevated of LiFePO4@C were improved by depositing α-Si film on the electrode. ► An oxide film at the silicon/electrolyte interface acts as a barrier to the interaction between the LiFePO4 and the electrolyte. ► The partially oxidized silicon atoms are expected to be capable of injecting electrons into the conduction band and generating a current at the end of the oxide dissolution induced by HF.

The electronic structures and magnetic properties of Zn1−xCoxO (x=5.55%,8.33%,12.5%x=5.55%,8.33%,12.5%) are studied using first-principles calculations in combination with Monte Carlo (MC) simulation. The combinational method makes possible a complete simulation from the microscopic magnetic interaction to macroscopic magnetic behavior. The calculated results from first principles indicate that the ferromagnetic ground state is stabilized by a half-metallic electronic structure which originates from the strong hybridization between Co 3d electrons and O 2p electrons. With the magnetic coupling strengths obtained from first-principles calculations, the MC simulation predicts the ferromagnetism of Zn1−xCoxO (x=5.55%,8.33%,12.5%x=5.55%,8.33%,12.5%) with Tc=220,360,530K, which is consistent with the experimental facts.

Based on Monte Carlo simulation, the magnetic properties of the Heisenberg face-centered cubic (fcc) multilayer films with competitive nearest neighbor (NN) and next-nearest neighbor (NNN) interactions are investigated. Four different kinds of magnetic phases and spin orderings depending on the relative signs and strengths of NN and NNN interactions are presented and discussed. A new 4×4 transfer matrix method which is used to calculate the phase transition of films with NN and NNN interactions is derived. In addition, different order parameters are constructed to characterize the transition in different systems, and a complete description of phase diagram displaying transitions between those various phases is also reported. Finally, it is found that the simulated results are consistent with those derived by 4×4 transfer matrix method.

Monte Carlo simulation studies are performed to examine influence of structure and interaction fluctuations on magnetic properties of a ferromagnetic system modelled with a Heisenberg Hamiltonian. It is found that the spontaneous magnetization at low temperature for the multilayered films decreases with temperature in a Bloch law of spin-wave excitations. Both Bloch coefficient B and exponent b vary evidently because of a strong surface and size effect in the finite magnetic films with free boundaries. For the disordered bulk FCC magnet with periodic boundary, the Bloch T3/2 law is followed at low temperature and B is greatly influenced by the structure and interaction fluctuations. At the same time, Bloch coefficient B of the amorphous magnet with the coordination and interaction fluctuations has been derived. The simulated results are in good agreement with the theoretical predictions of spin-wave excitation, and explain the experimental facts well.

Nano-crystalline FeOOH particles (5∼10 nm) have been uniformly mixed with electric matrix of single-walled carbon nanotubes (SWNTs) for forming FeOOH/SWNT composite via a facile ultrasonication method. Directly using the FeOOH/SWNT composite (containing 15 wt% SWNTs) as anode material for lithium battery enhances kinetics of the Li+ insertion/extraction processes, thereby effectively improving reversible capacity and cycle performance, which delivers a high reversible capacity of 758 mAh·g−1 under a current density of 400 mA·g−1 even after 180 cycles, being comparable with previous reports in terms of electrochemical performance for FeOOH anode. The good electrochemical performance should be ascribed to the small particle size and nano-crystalline of FeOOH, as well as the good electronic conductivity of SWNT matrix.Uniform FeOOH/SWNTs have been synthesized by a simple method and investigated as an anode material for lithium-ion batteries. FeOOH/SWNT composite produced large reversible capacities, long cyclabilities and excellent rate capabilities.Download full-size image

•Yolk-shell structured Fe3C/Fe3O4@C is prepared by hydrothermal reaction coupled with wet-chemical reduction.•The Fe3C/Fe3O4@C exhibit high specific capacity, good rate capability and cycle stability for LIBs.•The enhanced performance is ascribed to the C-shell and dispersed catalysts of Fe3C NPs.Most metal oxides with high theoretical specific capacities including Fe3O4 are promising lithium battery (LIB) anode materials, which capacities are larger than that of current commercial graphite. However, most of these anodes suffer from the defects of poor electronic conductivity, large volumetric expansion upon lithiation and low coulombic efficiency. Here, as a typical work, we develop and fabricate a novel composite of yolk-shell structured Fe3O4@C mixed with Fe3C catalysts directly used as LIB anodes. The anode of Fe3O4 nanospheres protected by the carbon shell and added with the Fe3C catalysts, can deliver obviously enhanced LIB performance. Especially, tested at 1000 mA g−1, the electrodes afforded high capacity of ∼600 mAh g−1 after 300 cycles at room temperature and high reversible capacity of ∼380 mAh g−1 even after 700 cycles at a relatively low temperature of 0 oC. The enhanced LIB performance could be associated with the contribution of carbon shell and Fe3C adding. These results revealed the potential applications of Fe3C/Fe3O4@C nanostructure materials as anodes for LIBs.Composites of yolk-shell Fe3C/Fe3O4@C are synthesized and used as high performance anode for lithium batteries.

In this paper, we investigate, by molecular dynamics simulations, the mechanical properties of a new carbon nanostructure, termed a graphene nanochain, constructed by sewing up pristine or twisted graphene nanoribbons (GNRs) and interlocking the obtained nanorings. The obtained tensile strength of defect-free nanochain is a little lower than that of pristine GNRs and the fracture point is earlier than that of the GNRs. The effects of length, width and twist angle of the constituent GNRs on the mechanical performance are analyzed. Furthermore, defect effect is investigated and in some high defect coverage cases, an interesting mechanical strengthening-like behavior is observed. This structure supports the concept of long-cable manufacturing and advanced material design can be achieved by integration of nanochain with other nanocomposites. The technology used to construct the nanochain is experimentally feasible, inspired by the recent demonstrations of atomically precise fabrications of GNRs with complex structures [Phys. Rev. Lett., 2009, 102, 205501; Nano Lett., 2010, 10, 4328; Nature, 2010, 466, 470].

Designing an efficient catalyst is essential to improve the electrochemical performance for Li–O2 batteries. In this study, the novel composites of Fe/Fe3C carbon nanofibers (Fe/Fe3C–CNFs) were synthesized via a facile electrospinning method and used as cathode catalysts for Li–O2 batteries. Owing to their favorable structures and desirable bifunctional catalytic activities, the resulting cathodes with a Fe/Fe3C–CNF catalyst exhibited superior electrochemical performance with high specific capacity, good rate capability and cycle stability. It is revealed that the synergistic effect of the fast kinetics of electron transport provided by the CNF support and the high electro-catalytic activity provided by the Fe/Fe3C composites resulted in the excellent performance for Li–O2 batteries. The preliminary result manifests that the composites of Fe/Fe3C–CNFs are promising cathode electrocatalysts for Li–O2 batteries.

Ternary spinel MFe2O4 (M = Co, Ni) nanoparticles coated on multi-walled carbon nanotubes (MFe2O4/CNTs) were prepared via a simple hydrothermal method. Owing to their favorable structures and desirable bi-functional oxygen reduction and evolution activities, the resulting MFe2O4/CNT (M = Co, Ni) composites as electrocatalysts for the cathodes deliver better electrochemical performance during the discharge and charge processes compared with that of the pure carbon of ketjen black (KB). The good performance can be attributed to the excellent catalytic activity of highly dispersed MFe2O4 (M = Co, Ni) nanoparticles and facile electron transport by supporting CNTs. This preliminary result manifests that the ternary spinel MFe2O4/CNT (M = Co, Ni) composites are promising cathode electrocatalysts for non-aqueous Li–O2 batteries.