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1.
Li4Ti5O12/Li2TiO3 composite nanofibers with the mean diameter of ca. 60 nm have been synthesized via facile electrospinning. When the molar ratio of Li to Ti is 4.8:5, the Li4Ti5O12/Li2TiO3 composite nanofibers exhibit initial discharge capacity of 216.07 mAh g?1 at 0.1 C, rate capability of 151 mAh g?1 after being cycled at 20 C, and cycling stability of 122.93 mAh g?1 after 1000 cycles at 20 C. Compared with pure Li4Ti5O12 nanofibers and Li2TiO3 nanofibers, Li4Ti5O12/Li2TiO3 composite nanofibers show better performance when used as anode materials for lithium ion batteries. The enhanced electrochemical performances are explained by the incorporation of appropriate Li2TiO3 which could strengthen the structure stability of the hosted materials and has fast Li+-conductor characteristics, and the nanostructure of nanofibers which could offer high specific area between the active materials and electrolyte and shorten diffusion paths for ionic transport and electronic conduction. Our new findings provide an effective synthetic way to produce high-performance Li4Ti5O12 anodes for lithium rechargeable batteries.  相似文献   

2.
Transport properties of ionic salt CsH5(PO4)2 are studied by the impedance method. The salt’s bulk conductivity ranges from 10?8 to 10?4 S cm?1 in the temperature interval 90 to 145°C. The apparent activation energy is high (1.6–2.0 eV). The conductivity is slightly anisotropic: it is maximum in the [001] direction and minimum in the [100] direction (~5.6 and 1 times × 10?6 S cm?1, respectively, at 130°C). The conductivity of polycrystalline samples is higher by 1–2 orders of magnitude, and the activation energy drops to 1.05 eV due to the formation of a pseudoliquid layer with a high proton mobility at the intercrystallite boundary. The salt’s thermodynamic properties are examined by differential scanning calorimetry and thermogravimetry. No phase transitions are discovered in the salt up to the melting point (151.6°C), with the melting enthalpy equal to ~34 kJ mol?1. The crystallization occurs at lower temperatures (107°C) and the crystallization enthalpy (?18 kJ mol?1) is lower than the melting enthalpy. The melting is accompanied by slow decomposition of the salt. Factors affecting the proton transport in the salt are analyzed.  相似文献   

3.
Li2ZnTi3O8/C nanocomposite has been synthesized using phenolic resin as carbon source in this work. The structure, morphology, and electrochemical properties of the as-prepared Li2ZnTi3O8 samples were analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscope (TEM), Raman spectroscopy (RS), galvanostatic charge–discharge, and AC impedance spectroscopy. SEM images show that Li2ZnTi3O8/C was agglomerated with a primary particle size of ca. 40 nm. TEM images reveal that a homogeneous carbon layer (ca. 5 nm) formed on the surface of Li2ZnTi3O8 particles which is favorable to improve the electronic conductivity and inhibit the growth of Li2ZnTi3O8 during annealing process. The as-prepared Li2ZnTi3O8/C composite with 6.0 wt.% carbon exhibited a high initial discharge capacity of 425 and 159 mAh g?1 at 0.05 and 5 A g?1, respectively. At a high current density of 1 A g?1, 95.5 % of its initial value is obtained after 100 cycles.  相似文献   

4.
Solid solutions based on cesium monogallate CsGaO2 are synthesized in the Ga2O3-TiO2-Cs2O system. Their crystalline structure and also temperature and concentration conductivity dependences are studied. The cesium cation character of conductivity is confirmed. The most conducting samples contain an excess of cesium oxide and have the structure of high-temperature γ-modification of KAlO2. Their specific conductivity is (5.0–6.7) × 10?3 S cm?1 at 400 °C, (2.5–5.0) × 10?2 S cm?1 at 700°C at the activation energy of 33–35 kJ/mol?1.  相似文献   

5.
Composites ZrO2-(Bi2CuO4+ 20 wt % Bi2O3) (50–80 vol % ZrO2) are synthesized and their physicochemical properties are studied. It is demonstrated that the composites comprise triple-phase mixtures of ZrO2 of a monoclinic modification, Bi2CuO4, and solid solution Bi2?x Zr x O3 + x/2 and retain their mechanical strength up to 800°C. Impedance spectroscopy is used to examine their electroconductivity at 700–800°C in the interval of partial oxygen pressures extending from 37 to 2.1 × 104 Pa. Contributions made by electronic and ionic constituents to their overall conductivity are evaluated. The best specimens’ conductivity is ~0.01 S cm?1, with the electronic and ionic transport numbers nearly equal. The composite consisting of 50 vol % ZrO2 and 50 vol % (Bi2CuO4 + 20 wt % Bi2CuO4) is tested in the role of an oxygen-separating membrane. The selective flux of oxygen in the temperature interval 750–800°C amounts to (2.2–6.3) × 10?8 mol cm?2 s?1, testifying that these materials may be used as gas-separating membranes.  相似文献   

6.
Lithium-vanadium oxide with the formal composition Li6V5O15, uniform microsctructure, and the particle size of 100 nm is synthesized by a solution method. The synthesized compound is characterized by the methods of X-ray diffraction analysis, Raman spectroscopy, and synchronous thermal analysis. The total electric conductivity is measured by the method of impedance spectroscopy and its electronic component is estimated by dc method. In the temperature range of 200–400°C, Li6V5O15 represents a mixed electronic- ionic conductor with predomination of the ionic component and is thermally stable up to 550°С. Preliminary tests of a laboratory model of electrochemical cell Li|LiPF6|Li6V5O15 are carried out.  相似文献   

7.
Electrical conductivity in the monoclinic Li2TiO3, cubic Li1.33Ti1.67O4, and in their mixture has been studied by impedance spectroscopy in the temperature range 20–730 °C. Li2TiO3 shows low lithium ion conductivity, σ300≈10–6 S/cm at 300 °C, whereas Li1.33Ti1.67O4 has 3×10–8 at 20 °C and 3×10–4 S/cm at 300 °C. Structural properties are used to discuss the observed conductivity features. The conductivity dependences on temperature in the coordinates of 1000/T versus logeT) are not linear, as the conductivity mechanism changes. Extrinsic and intrinsic conductivity regions are observed. The change in the conductivity mechanism in Li2TiO3 at around 500–600 °C is observed and considered as an effect of the first-order phase transition, not reported before. Formation of solid solutions of Li2– x Ti1+ x O3 above 900 °C significantly increases the conductivity. Irradiation by high-energy (5 MeV) electrons causes defects and the conductivity in Li2TiO3 increases exponentially. A dose of 144 MGy yields an increase in conductivity of about 100 times at room temperature. Electronic Publication  相似文献   

8.
RF3 and R0.95Sr0.05F2.95 (R = La, Ce, Pr, Nd) ceramic specimens were prepared by hot pressing at 1173 K under pressure of 3 × 108 Pa for 20 min. The ionic conductivity value was determined by means of impedance spectroscopy in vacuum from 293 to 823 K. For LaF3 at 350 K, the single crystal / ceramics conductivity ratio is about 5. The difference decreases at higher temperature and disappears about 500 K. The ionic conductivity activation energy is 0.30 ± 0.05 eV. For La0.95Sr0.05F2.95, the conductivity of ceramics below 500 K is slightly lower that of single crystals. At T > 500 K, the conductivity values of ceramic and single crystal specimens practically coincide. The ionic conductivity of hot pressed ceramics is about 10?2 S/cm at 500 K and activation energy is 0.25 ± 0.02 eV.  相似文献   

9.
All-solid-state rechargeable lithium-ion batteries (AS-LIBs) are attractive power sources for electrochemical applications due to their potentiality in improving safety and stability over conventional batteries with liquid electrolytes. Finding a solid electrolyte with high ionic conductivity and compatibility with other battery components is a key factor in raising the performance of AS-LIBs. In this work, we prepare argyrodite-type Li6PS5X (X = Cl, Br, I) using mechanical milling followed by annealing. X-ray diffraction characterization reveals the formation and growth of crystalline Li6PS5X in all cases. Ionic conductivity of the order of 7?×?10?4 S cm?1 in Li6PS5Cl and Li6PS5Br renders these phases suitable for AS-LIBs. Joint structure refinements using high-resolution neutron and laboratory X-ray diffraction provide insight into the influence of disorder on the fast ionic conductivity. Besides the disorder in the lithium distribution, it is the disorder in the S2?/Cl? or S2?/Br? distribution that we find to promote ion mobility, whereas the large I? cannot be exchanged for S2? and the resulting more ordered Li6PS5I exhibits only a moderate conductivity. Li+ ion migration pathways in the crystalline compounds are modelled using the bond valence approach to interpret the differences between argyrodites containing different halide ions.  相似文献   

10.
The Li(Ni0.33Co0.33Mn0.33)O2 (LNCMO) cathode material is prepared by poly(vinyl pyrrolidone) (PVP)-assisted sol-gel/hydrothermal and poly(ethylene glycol)-block-poly(propylene glycol)-block-poly (ethylene glycol) (Pluronic-P123)-assisted hydrothermal methods. The compound prepared by PVP-assisted hydrothermal method shows a comparatively higher electrical conductivity of ~2?×?10?5 S cm?1 and exhibits a discharge capacity of 152 mAh g?1 in the voltage range of 2.5 to 4.4 V, for a C-rate of 0.2 C, whereas the compounds prepared by P123-assisted hydrothermal method and PVP-assisted sol-gel method show a total electrical conductivity in the order of 10?6 S cm?1 and result in poor electrochemical performance. The structural and electrical properties of LNCMO (active material) and its electrochemical performance are correlated. The difference in percentage of ionic and electronic conductivity contribution to the total electrical conductivity is compared by transference number studies. The cation disorder is found to be the limiting factor for the lithium ion diffusion as determined from ionic conductivity values.  相似文献   

11.
Perovskite phases Ba3In2ZrO8 and Ba4In2Zr2O11 with the nominal concentration of structural oxygen vacancies 1/9 and 1/12, respectively, were synthesized by solid-phase and solution methods. X-ray diffraction showed cubic symmetry of both phases with the unit cell parameter a = 0.4193(2) and 0.4204(3) nm, respectively. The absence of superstructural lines resulted in the conclusion on statistical arrangement of oxygen vacancies. Thermogravimetry and mass spectrometry proved that both phases can reversibly absorb water from gas phase (pH2O = 2 × 10−2 atm) with observed correlation between the concentration of oxygen vacancies and amount of absorbed water. The total water amount was up to 0.9 mol per formula unit or, if recalculated for perovskite unit ABO3, 0.3 and 0.23 mol H2O, respectively. The temperature curves of coductivity in the atmosphere with various partial water vapor pressures (pH2O = 3 × 10−5 and 2 × 10−2 atm) showed significantly higher conductivity and lower activation energy (0.52 eV) in humid atmosphere due to proton transfer. The proton conductivity is up to 5 × 10−4 Ohm−1 cm−1 at 300°C for Ba3In2ZrO8 specimen. IR spectrometry showed that protons in the structure exist primarily in OH-groups.  相似文献   

12.
Sn-doped Li-rich layered oxides of Li1.2Mn0.54-x Ni0.13Co0.13Sn x O2 have been synthesized via a sol-gel method, and their microstructure and electrochemical performance have been studied. The addition of Sn4+ ions has no distinct influence on the crystal structure of the materials. After doped with an appropriate amount of Sn4+, the electrochemical performance of Li1.2Mn0.54-x Ni0.13Co0.13Sn x O2 cathode materials is significantly enhanced. The optimal electrochemical performance is obtained at x = 0.01. The Li1.2Mn0.53Ni0.13Co0.13Sn0.01O2 electrode delivers a high initial discharge capacity of 268.9 mAh g?1 with an initial coulombic efficiency of 76.5% and a reversible capacity of 199.8 mAh g?1 at 0.1 C with capacity retention of 75.2% after 100 cycles. In addition, the Li1.2Mn0.53Ni0.13Co0.13Sn0.01O2 electrode exhibits the superior rate capability with discharge capacities of 239.8, 198.6, 164.4, 133.4, and 88.8 mAh g?1 at 0.2, 0.5, 1, 2, and 5 C, respectively, which are much higher than those of Li1.2Mn0.54Ni0.13Co0.13O2 (196.2, 153.5, 117.5, 92.7, and 43.8 mAh g?1 at 0.2, 0.5, 1, 2, and 5 C, respectively). The substitution of Sn4+ for Mn4+ enlarges the Li+ diffusion channels due to its larger ionic radius compared to Mn4+ and enhances the structural stability of Li-rich oxides, leading to the improved electrochemical performance in the Sn-doped Li1.2Mn0.54Ni0.13Co0.13O2 cathode materials.  相似文献   

13.
The novel Li3V2(PO4)3 glass-ceramic nanocomposites were synthesized and investigated as electrodes for energy storage devices. They were fabricated by heat treatment (HT) of 37.5Li2O–25V2O5–37.5P2O5?mol% glass at 450 °C for different times in the air. XRD, SEM, and electrochemical methods were used to study the effect of HT time on the nanostructure and electrochemical performance for Li3V2(PO4)3 glass-ceramic nanocomposites electrodes. XRD patterns showed forming Li3V2(PO4)3 NASICON type with monoclinic structure. The crystalline sizes were found to be in the range of 32–56 nm. SEM morphologies exhibited non-uniform grains and changed with variation of HT time. The electrochemical performance of Li3V2(PO4)3 glass-ceramic nanocomposites was investigated by using galvanostatic charge/discharge methods, cyclic voltammetry, and electrochemical impedance spectroscopy in 1 M H2SO4 aqueous electrolyte. The glass-ceramic nanocomposites annealed for 4 h, which had a lower crystalline size, exhibited the best electrochemical performance with a specific capacity of 116.4 F g?1 at 0.5 A g?1. Small crystalline size supported the lithium ion mobility in the electrode by decreasing the ion diffusion pathway. Therefore, the Li3V2(PO4)3 glass-ceramic nanocomposites can be promising candidates for large-scale industrial applications in high-performance energy storage devices.  相似文献   

14.
Vanadium pentoxide (V2O5) nanofibers (NFs) with a thin carbon layer of 3–5 nm, which wrapped on V2O5 nanoparticles, and integrated multiwalled carbon nanotubes (MWCNTs) have been fabricated via simple electrospinning followed by carbonization process and post-sintering treatment. The obtained composite displays a NF structure with V2O5 nanoparticles connected to each other, and good electrochemical performance: delivering initial capacity of 320 mAh g?1 (between 2.0 and 4.0 V vs. Li/Li+), good cycling stability (223 mAh g?1 after 50 cycles), and good rate performance (~?150 mAh g?1 at 2 A g?1). This can attribute to the carbon wrapped on the V2O5 nanoparticles which can not only enhance the electric conductivity to decrease the impendence of the cathode materials but also maintain the structural stability to protect the nanostructure from the corruption of electrolyte and the strain stress due to the Li-ion intercalation/deintercalation during the charge/discharge process. And, the added MWCNTs play the role of framework of the unique V2O5 coated by carbon layer and composited with MWCNT NFs (V2O5/C@MWCNT NFs) to ensure the material is more stable.  相似文献   

15.
The phase composition has been studied and an equilibrium phase diagram has been designed for the Al2O3-Li2O-R2O5 (R = Ta or Nb) systems in the subsolidus region up to 1000°C and 85 mol % Li2O. New phases with the composition Li1+x Al1?x O2?x , where x = 0–0.67, have been found.  相似文献   

16.
LiNi0.80Co0.15Al0.05O2 (NCA) is explored to be applied in a hybrid Li+/Na+ battery for the first time. The cell is constructed with NCA as the positive electrode, sodium metal as the negative electrode, and 1 M NaClO4 solution as the electrolyte. It is found that during electrochemical cycling both Na+ and Li+ ions are reversibly intercalated into/de-intercalated from NCA crystal lattice. The detailed electrochemical process is systematically investigated by inductively coupled plasma-optical emission spectrometry, ex situ X-ray diffraction, scanning electron microscopy, cyclic voltammetry, galvanostatic cycling, and electrochemical impedance spectroscopy. The NCA cathode can deliver initially a high capacity up to 174 mAh g?1 and 95% coulombic efficiency under 0.1 C (1 C?=?120 mA g?1) current rate between 1.5–4.1 V. It also shows excellent rate capability that reaches 92 mAh g?1 at 10 C. Furthermore, this hybrid battery displays superior long-term cycle life with a capacity retention of 81% after 300 cycles in the voltage range from 2.0 to 4.0 V, offering a promising application in energy storage.  相似文献   

17.
NMR (19F, 1H) methods are used to study ionic mobility in heptafluorozirconate (NH4)2.4Rb0.6ZrF7 in a range of temperatures from 150 K to 430 K. Types of ionic movements are determined, and their activation energy is evaluated. As a result of a phase transition a modification forms in which diffusion in the ammonium sublattice and isotropic reorientations of ZrF 7 3? complex anions are observed. According to preliminary data, due to diffusion of ammonium ions the compound has relatively high ionic conductivity (σ ≈ 8.3 × 10?5 S/cm at 423 K).  相似文献   

18.
Ce2O3-K2O-P2O5 ternary system has been investigated by thermoanalytical methods (DTA, DSC), powder X-ray diffraction, XPS and IR spectroscopy. The existence of three double potassium-cerium(III) phosphates has been confirmed and a new binary phosphate K4Ce2P4O15 has been found. Phase diagram and isothermal section at room temperature of the system Ce2O3-K2O-P2O5 have been presented.  相似文献   

19.
Li5SiN3 crystals are synthesized by direct reaction between Li3N and Si3N4 with the molar ratio Li3N/Si3N4 of 10:1. Reaction is performed at 1073 K for 1 h under a nitrogen atmosphere of 700 Torr. The lattice constant determined by the X-ray powder diffraction method is 4.718 Å. Four broad Raman peaks are observed at 196, 286, 580, and 750 cm?1. By analogy with LiMgN, the broad peak at 580 cm?1 with a half width of 140 cm?1 is attributed to homogenously random distribution of Li and Si atoms. The band gap of Li5SiN3 is found to be a direct gap of about 2.5 eV by optical absorption and photoacoustic spectroscopy methods. Comparison with the conventional cathode materials for lithium ion batteries, this gap value is close to d-d transition energy of Mn in LiMn2O4 (1.63 eV or 2.00 eV) and that of Co in LiCoO2 (2.1 eV), suggesting that Li5SiN3 is a possible cathode material. The 5 × 5 mm2-sized lithium secondary battery of Li5SiN3 cathode/propylene carbonate + LiClO4 electrolyte/Li anode structure shows a discharge capacity of 2.4 μAh cm?2 for a discharge current of 1.0 μA.  相似文献   

20.
The subsolidus region of the Li2O-MgO-B2O3 system has been studied by X-ray powder diffraction and differential thermal analysis. Isothermal sections at 500–550 and 650–700°C have been designed. The following complex borates have been found to form: at 500–550°C, Li2MgB2O5 and LiMgBO3 are formed; at 650–700°C, a new phase Li4MgB2O5 is formed along with LiMgBO3; and at 5500–600°, Li2MgB2O5 is formed.  相似文献   

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