Youzhong Dong

Hydrothermal Synthesis and Electrochemical Properties of Li3V2(PO4)3/C-Based Composites for Lithium-Ion Batteries

To improve performance at higher rates, we developed a hydrothermal method to prepare carbon-coated monoclinic lithium vanadium phosphate (Li(3)V(2)(PO(4))(3)) powder to be used as a cathode material for Li-ion batteries. The structural, morphological and electrochemical properties were characterized by X-ray diffraction (XRD), scanning and transmission electron microscopy (SEM and TEM), and galvanostatic charge-discharge cycling. A superior cycle and rate behavior are demonstrated for Li(3)V(1.85)Sc(0.15)(PO(4))(3)/C and Li(2.96)Ca(0.02)V(2)(PO(4))(3)/C electrodes at charge-discharge current rates above 5C.

First-principles study of intrinsic vacancy defects in Sr2MgSi2O7 phosphorescent host material

Electronic structures of intrinsic vacancy defects in Sr2MgSi2O7 phosphorescent host material are investigated using first-principles calculations. Si vacancies are too high in energy to play any role in the persistent luminescence of Sr2MgSi2O7 phosphor. Mg vacancies form easier than Sr vacancies as a result of strain relief. Among all the vacancies, O1 vacancies stand out as a likely candidate because they are the most favorable in energy and introduce an empty triply degenerate state just below the CBM and a fully-occupied singlet state at ~1 eV above the VBM, constituting in this case effective hole trap level and electron trap levels, respectively. Mg vacancies are unlikely to explain the persistent luminescence because of its too shallow electron trap level but they may compensate the hole trap associated with O1 vacancies. We yield consistent evidence for the defect physics of these vacancy defects on the basis of the equilibrium properties of Sr2MgSi2O7, total-energy calculations, and electronic structures. The persistent luminescence mechanism of Sr2MgSi2O7:Eu2+, Dy3+ phosphor is also discussed based on our results for O1 vacancies trap center. Our results provide a guide to more refined experiments to control intrinsic traps, whereby probing synthetic strategies toward new improved phosphors.

Crystal structure and electrochemical properties of LiFe 1− x Zn x PO 4 ( x ≤ 1.0)

A series of LiFe 1− x Zn x PO 4 (0.0 ≤ x ≤ 1.0) compounds were prepared by solid-state reaction. Effects of the substitution of Zn for Fe on crystal structure and electrochemical properties of LiFe 1− x Zn x PO 4 were investigated. The results show that single-phase regions of LiFe 1− x Zn x PO 4 with orthorhombic (space group Pmna ) and monoclinic ( Cc ) structures were found for the compounds with low Zn (or high Fe) contents of 0.0 ≤ x ≤ 0.30 and high Zn (or low Fe) contents of 0.90 ≤ x ≤ 1.0, respectively. The LiFe 1− x Zn x PO 4 compounds with medium Zn (or Fe) contents of 0.35 ≤ x ≤ 0.80 are two-phase mixtures containing both the orthorhombic and the monoclinic phases. Systematic variations of unit-cell parameters a , b , c , and volume V with the Zn content determined by X-ray diffraction have also been obtained. Our electrochemical study show that the conductivity of LiFe 1− x Zn x PO 4 increases by almost 2 orders of magnitude from 2.13 × 10 −9 to 1.27 × 10 −7 Scm −1 as the Zn content increasing from x = 0 to 0.3. The initial specific capacity decreases and the cycle performance increase with increasing Zn-doping content in the four orthorhombic LiFe 1− x Zn x PO 4 compounds. Among the four LiFe 1− x Zn x PO 4 compounds, LiFe 0.8 Zn 0.2 PO 4 has the highest capacity retentions after 6 to 20 cycles and the capacity retention is 93.7% after 20 cycles, even though the initial discharge specific capacity of LiFe 0.8 Zn 0.2 PO 4 is lower than those of LiFeZnPO 4 and LiFe 0.9 Zn 0.1 PO 4 . LiFe 0.7 Zn 0.3 PO 4 has the highest capacity retention of 97% after 20 cycles.

Mo6+ Doping in Li3VO4 Anode for Li-Ion Batteries: Significantly Improve the Reversible Capacity and Rate Performance

Consider the almost insulator for pure Li3VO4 with a band gap of 3.77 eV, to significantly improve the electrical conductivity, the novel Li3V1-xMoxO4 (x = 0.00, 0.01, 0.02, 0.05, and 0.10) anode materials were prepared successfully by simple sol-gel method. Our calculations show that, by substitute Mo6+ for V5+, the extra electron occupied the V 3p empty orbital and caused the Fermi level shift up into the conduction band, where the Mo-doped Li3VO4 presents electrical conductor. The V/I curve measurements show that, by Mo doping in V site, the electronic conductivity of the Li3VO4 was increased by 5 orders of magnitude. And thence the polarization was obviously reduced. EIS measurement results indicated that by Mo-doping a higher lithium diffusion coefficient can be obtained. The significantly increased electronic conductivity combined the higher lithium diffusion coefficient leads to an obvious improvement in reversible capacity and rate performance for the Mo-doped Li3VO4. The resulting Li3V1-xMoxO4 (x = 0.01) material exhibited the excellent rate capability. At a high rate 5 C, a big discharge capacity of the initial discharge capacity 439 mAh/g can be obtained, which is higher than that of pure Li3VO4 (only 166 mAh/g), and after 100 cycles the mean capacity fade is only 0.06% per cycle.

Cheese-like bulk carbon with nanoholes prepared from egg white as an anode material for lithium and sodium ion batteries

Cheese-like bulk carbon with nanoholes has been successfully fabricated from egg white via a simple annealing method by using distilled water as a green clean “corrosive agent”. X-ray diffractions and SEM images show the decomposition product of boiled egg white after annealing is bulk carbon, containing NaCl and KCl with a trace amount of nitrogen doping. After ultrasonic washing and centrifugation, the distilled water removed the NaCl and KCl nanocrystals from the bulk carbon completely and retained empty spaces, which eventually leads to the formation of a cheese-like structured bulk carbon with nanoholes. Our electrochemical tests show this cheese-like bulk carbon with nanoholes has a high specific capacity and good cycling performance and rate stability when evaluated as an anode material for lithium-ion batteries. Meanwhile, the electrochemical performances as an anode material for a sodium-ion battery are also displayed for comparison.

Synthesis and structural data of a Fe-base sodium metaphosphate compound,NaFe(PO3)3

This data article contains the synthesis and structure information of a new Fe-base sodium metaphosphate compound, which is related to the research article entitled ‘Synthesis, structural, magnetic and sodium deinsertion/insertion properties of a sodium ferrous metaphosphate, NaFe(PO3)3’ by Lin et al. [1]. The research article has reported a new Fe-base metaphosphate compound NaFe(PO3)3, which is discovered during the exploration of the new potential electrode materials for sodium-ion batteries. In this data article, the synthesized process of this metaphosphate compound and the morphology of the obtained sample will be provided. The high-power XRD Rietveld refinement is applied to determine the crystal structure of this metaphosphate compound and the refinement result including the main refinement parameters, atomic coordinate and some important lattace parameters are stored in the cif file. Also, the refined structure has be evaluated by checkcif report and the result is also provided as the supplementary materials.

Model of V Hg Incorporation in Arsenic-Doped HgCdTe: First-Principles Calculations

Following the suggestion that the AsHg–VHg and AsHg–2VHg defect complexes are potential sources of carrier compensation observed in As-doped HgCdTe, we have studied the electronic properties and formation energies of these complexes. We find that these complexes are electrically active acceptors but have exceedingly high formation energies, meaning that they play no role in carrier compensation except at low temperatures. VHg will thus likely remain as an isolated defect. Such a model of VHg incorporation allows us to further predict the postgrowth As activation. Our prediction emphasizes the AsHg–2VHg complex as the starting defect for As activation, rather than the AsHg–VHg pair as previously suggested.

Superstructure ZrV2O7 nanofibres: thermal expansion, electronic and lithium storage properties

ZrV2O7 has attracted much attention as a negative thermal expansion (NTE) material due to its isotropic negative structure. However, rarely has investigation of the lithium storage behaviors been carried out except our first report on it. Meanwhile, the electrochemical behaviors and energy storage characteristics have not been studied in depth and will be explored in this article. Herein, we report on the synthesis, characterization and lithium intercalation mechanism of superstructure ZrV2O7 nanofibres that were prepared through a facile solution-based method with a subsequent annealing process. The thermal in situ XRD technique combined with the Rietveld refinement method is adopted to analyze the change in the temperature-dependent crystal structure. Benefiting from the nanostructured morphology and relatively high electronic conductivity, it presents acceptable cyclic stability and rate capability. According to the operando evolution of the XRD patterns obtained from electrochemical in situ measurements, the Li intercalation mechanism of the solid solution process with a subsequent conversion reaction can be concluded. Finally, the amorphous state of the electrodes after the initial fully discharged state can effectively enhance the electrochemical performances.