Ionic conductivity of isostructural crystals of the superionic conductors Li3Fe2(PO4)4 and Li3Sc2(PO4)3

The results of measurements of the ionic conductivity σ in Li₃M₂(PO₄)₃ (M=Fe, Sc) single crystals along various crystallographic directions are analyzed. Possible causes of the different behavior of σ in the isostructural crystals are discussed: a jump of the conductivity in the transition to the superionic phase in Li₃Sc₂(PO₄)₃ and its absence in Li₃Fe₂(PO₄)₃; the existence of a conductivity maximum in different crystallographic directions (along the c axis in Li₃Sc₂(PO₄)₃ and along the a axis in Li₃Fe₂(PO₄)₃). Fiz. Tverd. Tela (St. Petersburg) 39, 83–86 (January 1997)     

Structural and electrical characterization of the NASICON-type Li2FeZr(PO4)3 and Li2FeTi(PO4)3 compounds

In order to develop new electrolytes for all-solid-state rocking chair lithium batteries, the NASICON-type compounds Li₂FeZr(PO₄)₃ and Li₂FeTi(PO₄)₃ were investigated by powder X-ray diffraction technique and impedance spectroscopy. Li₂FeZr(PO₄)₃ is orthorhombic Pbna (a=8.706(3), b=8.786(2), c=12.220(5) Å) and Li₂FeTi(PO₄)₃ is orthorhombic Pbca (a=8.557(3), b=8.624(3), c=23.919(6) Å). They show no phase transitions from RT to 800 °C. In the same temperature range logσT vs. 1/T show no slope variations. The activation energies for the ionic conductivity were 0.62 and 0.64 eV for Li₂FeTi(PO₄)₃ and Li₂FeTi(PO₄)₃, respectively. In order to better evaluate the present results they were compared with those of α and β-LiZr₂(PO₄)₃ phases, which were also prepared and characterised. A change of activation energy from 0.47 eV to 1.03 eV was observed in the case of β phase, at about 300 °C; attributed to the β (orthorhombic) ? β′ (monoclinic) phase transition. In the α phase the activation energy 0.47 eV in the temperature range 150 – 850 °C. The Li₂FeZr(PO₄)₃ and Li₂FeTi(PO₄)₃ compounds can be interesting for applications as solid electrolytes in high temperature (>300 °C) lithium batteries.     

Glass transition (Tg) and dielectric loss in Na3PO4–Pb3(PO4)2–BiPO4 phosphate glasses

Thermal and dielectric loss properties of Na₃PO₄-Pb₃(PO₄BiPO₄ (Na₂O-PbO-Bi₂O₃-P₂O₅) phosphate glasses, have been studied by the differential scanning calorimetry (DSC) and electrical factor loss (tgδ) measurements. Experiments have been carried out from ambient temperature to 500°C and show a strong influence of sodium ions on T_g and tgδ.     

C-rate and temperature dependence of electrochemical performance of Li[Co0.1Ni0.15Li0.2Mn0.55]O2 cathode materials before and after Co3(PO4)2 coating

Li[Co_0.1Ni_0.15Li_0.2Mn_0.55]O₂ was synthesized, as a cathode material with high capacity, by a simple combustion method followed by annealing at 800?°C. Li[Co_0.1Ni_0.15Li_0.2Mn_0.55]O₂ cathode materials were coated with lithium-active Co₃(PO₄)₂ to improve the electrochemical performance of rechargeable lithium batteries. Morphologies and physical properties of Li[Co_0.1Ni_0.15Li_0.2Mn_0.55]O₂ before and after the Co₃(PO₄)₂ coating were analyzed with a scanning electron microscope equipped with an energy dispersive X-ray spectroscope. Transmission electron microscopy, powder X-ray diffraction, and Brunauer?CEmmett?CTeller surface area analyses were also carried out. The electrochemical performances of Li[Co_0.1Ni_0.15Li_0.2Mn_0.55]O₂ cathode material before and after Co₃(PO₄)₂ coating were evaluated by galvanostatic charge?Cdischarge testing at different charge and discharge densities. The temperature dependence of the cathode material before and after Co₃(PO₄)₂ coating was investigated at 0, 10, 20, 30, 40, and 50?°C at a rate of 0.1?C. Co₃(PO₄)₂-Li[Co_0.1Ni_0.15Li_0.2Mn_0.55]O₂ exhibited good electrochemical performance under high C-rate and experimental temperature conditions. The enhanced electrochemical performances were attributed to the formation of a lithium-active Co₃(PO₄)₂-coating layer on Li[Co_0.1Ni_0.15Li_0.2Mn_0.55]O₂.     

Preparation of Li3V2 (PO4)3/LiFePO4 composite cathode material for lithium ion batteries

A novel process was attempted for synthesis of Li₃V₂ (PO₄)₃/LiFePO₄ composite cathode material via loading nano-LiFePO₄ (LFP) powders onto the outside of micrometer-size spherical Li₃V₂ (PO₄)₃ (LVP). The precursor of nano-LFP and LVP were synthesized via “controlled crystallization” and “spray drying” techniques, respectively. The X-ray diffraction characterization, scanning electron microscopy, and electrochemical performance measurements were studied. The results indicated that the prepared Li₃V₂(PO₄)₃/LiFePO₄ (LVP/LFP) composite material exhibited better discharging capacity at high C rate and at low temperature than that of LFP and bulk LVP/LFP. This can pave an effective way to improve the performance of LFP at high C rate and at low temperature.     

Potentiometric carbon dioxide sensor based on thin Li3PO4 electrolyte and Li2CO3 sensing electrode

Potentiometric CO₂ gas sensors with thin-film lithium phosphate (Li₃PO₄) electrolytes were developed by using radio frequency (RF) magnetron sputtering. Li₂CO₃ and a mixture of Li₂TiO₃ and TiO₂ were used as sensing and reference electrodes, respectively. By using the RF sputtering deposition process, we obtained a dense, crystalline, thin-film Li₃PO₄ electrolyte with good adhesion on the Al₂O₃ substrate. The thin-film Li₃PO₄ electrolyte had good ionic conductivity, i.e., 2.15?×?10^?6 S cm^?1 at 500 °C, and its activation energy was 0.97 eV. The thin-film Li₃PO₄ electrolyte was suitable for the miniaturization of potentiometric CO₂ sensors. The thin-film potentiometric CO₂ sensor provided relatively good sensing response for overall CO₂ concentrations (500 to 3,000 ppm and 5 to 20 %) at 500 °C. The Nernstian slope of 78.2 mV/decade obtained for CO₂ concentrations from 5 to 20 % at 500 °C was close to the theoretical value (76.6 mV/decade). Although the sensor’s reading deviated from the theoretical value at low CO₂ concentrations (500 to 3,000 ppm), the sensor provided better sensing performance than a potentiometric CO₂ sensor with a thick electrolyte. As a result, it was assumed that the thin-film sensor could be used to monitor the overall concentration of CO₂ in the environment.     

Three-dimensionally ordered composite electrode between LiMn2O4 and Li1.5Al0.5Ti1.5(PO4)3

A novel electrode system composed of three-dimensionally ordered macroporous (3DOM) Li_1.5Al_0.5Ti_1.5(PO₄)₃ (LATP) and LiMn₂O₄ was fabricated by the colloidal crystal templating method and sol–gel process. A LATP nanoparticle for the fabrication of 3DOM-LATP was prepared by a sol–gel process. A suspension containing polystyrene (PS) beads and the LATP nanoparticles was filtrated by using a polycarbonate filter to accumulate PS beads and LATP. The accumulated PS beads had a close-packing structure, and the void between PS beads was filled with LATP nanoparticles. 3DOM-LATP was obtained by heat treatment of the accumulated composite. Li–Mn–O sol was injected by a vacuum impregnation process into the macropores of 3DOM-LATP and then was heated to form three-dimensionally ordered composite materials consisting of LiMn₂O₄ and LATP. The formation of the composite between 3DOM-LATP and LiMn₂O₄ were confirmed with scanning electron microscopy and X-ray diffraction method. The prepared composite electrode system exhibited a good electrochemical performance. Paper presented at the 11th EuroConference on the Science and Technology of Ionics, Batz-sur-Mer, Sept. 9–15, 2007.     

Vibrational spectroscopic study of lithium intercalation into LiTi2(PO4)3

Ex situ vibrational spectra are recorded during the first discharge of LiTi₂(PO₄)₃. Spectral changes are consistent with a two-phase model for the electrochemical insertion of Li⁺ ions. Differences in the frequencies and relative intensities of the LiTi₂(PO₄)₃ and Li₃Ti₂(PO₄)₃ bands are due to changes in the effective force constants, dipole moment derivatives, and polarizability derivatives as Li⁺ is inserted into LiTi₂(PO₄)₃. The intramolecular PO₄³⁻ bending modes (ν₂ and ν₄) are found to be more sensitive to Li⁺ insertion than the intramolecular PO₄³⁻ stretching modes (ν₁ and ν₃). This is because ν₂ and ν₄ are less localized than ν₁ or ν₃ and are more susceptible to small structural changes in the unit cell. Furthermore, a band at 487 cm^− 1 appears in the infrared spectrum of Li₃Ti₂(PO₄)₃. This band is assigned as a Li⁺ ion cage mode and is due to Li⁺ ions that occupy the M(3) and M′(3) sites in the Li₃Ti₂(PO₄)₃ structure. A small degree of band broadening is also detected in the vibrational spectra when Li⁺ ions are inserted, which might indicate some disordering in the cathode material.     

XPS and ionic conductivity studies on Li1.3Al0.15Y0.15Ti1.7(PO4)3 ceramics

Li_1.3Al_0.15Y_0.15Ti_1.7(PO₄)₃ compound was synthesized by solid-state reaction, and ceramics were sintered. The surfaces of the ceramics were investigated by scanning electron microscopy and X-ray photoelectron spectroscopy. Li_1.3Al_0.15Y_0.15Ti_1.7(PO₄)₃ samples were tested in solid galvanic cells Ag|O₂+CO₂|Li₂CO₃|Li_1.3Al_0.15Y_0.15Ti_1.7(PO₄)₃|LiMnO₂+Mn₂O₃|O₂|Ag. The electromotive force measurements of this cell indicated that investigated samples are practically pure Li-ion conductors. Impedance spectroscopy studies have been performed in the frequency range 10^?2–3·10⁹ Hz and temperatures from ?57 °C to 334 °C. Three dispersion regions related to Li⁺ ionic transport in bulk, grain boundaries of the ceramics and to polarization of electrodes have been found. Total conductivity changes according to Arrhenius law in the studied temperature range, but an anomalous behavior was observed for the bulk conductivity of the ceramics.     

Li3V2(PO4)3 modified LiFePO4/C cathode materials with improved high-rate and low-temperature properties

LiFePO₄/C surface modified with Li₃V₂(PO₄)₃ is prepared with a sol–gel combustion method. The structure and electrochemical behavior of the material are studied using a wide range of techniques such as X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscope, galvanostatic charge–discharge, and electrochemical impedance spectroscopy. It is found that LiFePO₄/C surface modified with Li₃V₂(PO₄)₃ has the better electrochemical performance. The discharge capacity of the as-prepared material can reach up to 153.1, 137.7, 113.6, and 93.3 mAh g^?1 at 1, 2, 5, and 10 C, respectively. The capacitance of the LiFePO₄/C modified by Li₃V₂(PO₄)₃ is higher under lower discharging rate at ?20 °C, and the initial discharge capacity of 0.2 C is 131.4 mAh g^?1. It is also demonstrated that the presence of Li₃V₂(PO₄)₃ in the sample can reduce the charge transfer resistance in the range of ?20 to 25 °C, resulting in the enhanced electrochemical catalytic activity.     

Electrochemical properties and structures of the mixed-valence lithium cuprates Li3Cu2O4 and Li2NaCu2O4

The electrochemical performances of Li₃Cu₂O₄ and Li₂NaCu₂O₄ as cathode materials in lithium coin type batteries have been studied. In Li₃Cu₂O₄, the copper was oxidised to the III level when cycling. The replacement of the lithium by the sodium ions in the octahedral sites in Li₂NaCu₂O₄ might have an effect on the pathway of the lithium ions during the (de)intercalations. Paper presented at the 7th Euroconference on Ionics, Calcatoggio, Corsica, France, Oct. 1–7, 2000.     

Structural and dielectric properties of Pb(Li1/4Dy1/4W1/2)O3

The polycrystalline samples of Pb(Li_1/4Dy_1/4W_1/2)O₃ have been synthesized by high-temperature solid-state reaction techniques. Room temperature X-ray diffraction (XRD) studies of the compound provided preliminary structural data, and hence formation of a single phase desired material was confirmed. Detailed studies of dielectric constant (ε) and loss (tanδ) as a function of frequency (100 Hz to 10 kHz) at room temperature (298 K) and also as a function of temperature (liquid nitrogen to 403 K) at 10 kHz suggest that the compound undergoes a ferroelectric phase transition of diffuse type.     

Synthesis of flower-like Li3V2(PO4)3/C cathode with mixed morphology for advanced lithium-ion batteries

A rheological phase-assisted ball milling method was developed to synthesize of flower-like Li₃V₂(PO₄)₃/C composites consisting of nanofibers and nanoplate porous microstructure. The flower-like Li₃V₂(PO₄)₃/C composite delivered specific capacities of 120 and 108 mAh g^?1 at 0.5 and 10 C rates, respectively. A capacity retention of 99.5 % was sustained after 100 cycles at a 10-C cycling rate. The remarkable performance was attributed to the porous nanostructures that provide short electron/ion diffusion distance and large electrode/electrolyte contact area.     

(1-x)MgAl2O4-xTiO2 dielectrics for microwave and millimeter wave applications

The MgAl₂O₄ ceramics were prepared by the conventional solid-state ceramic route and the dielectric properties studied in the microwave frequency region (3–13 GHz). The phase purity and crystal structure were identified using the X-ray diffraction technique. The MgAl₂O₄ spinel ceramics show interesting microwave dielectric properties (ε_r=8.75, Q_uxf=68900 GHz (loss tangent = 0.00017 at 12.3 GHz), τ_f=-75 ppm/°C). The MgAl₂O₄ has high negative τ_f, which precludes its immediate use in practical applications. Hence the microwave dielectric properties of MgAl₂O₄ spinels were tailored by adding different mole fractions of TiO₂. The ε_r and Q factor of the mixed phases were increased with the molar addition of TiO₂ into the spinel to form mixtures based on (1-x)MgAl₂O₄-xTiO₂ (x=0.0-1.0). For x=0.25 in (1-x)MgAl₂O₄-xTiO₂, the microwave quality factor reaches a maximum value of Q_uxf=105400 GHz (loss tangent = 0.00007 at 7.5 GHz) where ε_r and τ_f are 11.035 and -12 ppm/°C, respectively. The microwave dielectric properties of the newly developed 0.75MgAl₂O₄-0.25TiO₂ dielectric is superior to several commercially available low loss dielectric substrates. PACS 77.22.-d; 84.40.-x; 81.05.Je     

Luminescence spectroscopy and electronic structure of ZrP2O7 and KZr2(PO4)3 crystals

The photoluminescence (PL) of ZrP₂O₇ and KZr₂(PO₄)₃ phosphate crystalline micro-powders grown by spontaneous crystallization method is studied under vacuum ultra-violet (VUV) synchrotron radiation excitations (4–20 eV region of excitation photon energies) in 8–300 K temperature region. The electronic structures (partial densities of states) and optical absorbance spectra of the crystals are calculated by the Full-Potential Linear Augmented Plane Wave Method. Both phosphate crystals reveal PL emission band in the UV spectral region peaking near 300 and 295 nm for ZrP₂O₇ and KZr₂(PO₄)₃ respectively. The spectral profile of the band weakly depends on temperature. The excitation spectra of the UV emission in each crystal contain intensive excitation band peaking at 189 and 182 nm for ZrP₂O₇ and KZr₂(PO₄)₃ respectively. The excitation band of the UV emission is related to band-to-band electronic transitions with charge transfer from O 2p to Zr 4d states. The energy band gaps E_g of ZrP₂O₇ and KZr₂(PO₄)₃ are estimated as 6.7 and 6.6 eV respectively.     

Crystal structure of di-(L-serine) phosphate monohydrate [C3O3NH7]2H3PO4H2O

The crystal structure of di-(L-serine) phosphate monohydrate [C₃O₃NH₇]₂H₃PO₄H₂O is determined by single-crystal x-ray diffraction. The intensities of x-ray reflections are measured at temperatures of 295 and 203 K. The crystal structure is refined using two sets of intensities. It is established that, in the structure, symmetrically nonequivalent molecules of L-serine occur in two forms, namely, the monoprotonated positively charged molecule CH₂(OH)CH(NH₃)⁺COOH and the zwitterion CH₂(OH)CH(NH₃)⁺COO^?, which are linked with each other and with the H₂PO ^?₄ ion through a hydrogen-bond system involving water molecules.

     

Phase evolution, Raman spectroscopy and microwave dielectric behavior of (Li1/4Nb3/4) doped ZrO2-TiO2 system

The phase evolution, Raman spectroscopy and microwave dielectric properties of (Li_1/4Nb_3/4) doped ZrO₂-TiO₂ system were investigated. The effects of the Zr/Ti ratio and the (Li_1/4Nb_3/4) substitution were addressed. X-ray diffraction and electron diffraction analysis showed that the crystalline phases of the (Li_1/4Nb_3/4) doped ZrO₂-TiO₂ ceramics depended greatly on the Zr/Ti ratio. The sample with Zr/Ti ratio of 7/9 crystallized as Zr₅Ti₇O₂₄ phase structure, a commensurate structure with a tripled a-axis superstructure and a Z^TTZ_TT sequence. Secondary phase of monoclinic ZrO₂ phase appeared when the Zr/Ti ratio was as high as 9/7. Raman analysis showed that the Raman peaks located at 651 and 624 cm⁻¹ were assigned to the vibration modes of Zr-O octahedron and Ti-O octahedron, respectively. The dielectric constant and quality factor (Qf value) of the (Li_1/4Nb_3/4) doped ZrO₂-TiO₂ ceramics decreased slightly as the Zr/Ti ratio changed from 6/10 to 9/7. The temperature coefficient of resonate frequency (TCF value) was sensitive to the Zr/Ti ratio and it showed a negative value when the Zr/Ti ratio was close to 5:7. Meanwhile, the TCF value of ZrO₂-TiO₂ ceramics could also be tailored by the (Li_1/4Nb_3/4) substitution.     

Low- and infralow-frequency dielectric properties of the Pb(Mg1/3Nb2/3)O3 + 2 wt % Li2O ceramics

A dielectric response of the Pb(Mg_1/3Nb_2/3)O₃ ferroelectric ceramics with impurity of 2 wt % Li has been studied. The phase transition has been found to exhibit a relaxor character, as is the case in PMN without Li. However, unlike pure PMN, the dielectric response dispersion in PMN + 2 wt % Li₂O has been described by the Cole-Cole equation at temperatures below the temperature of the low-frequency maximum of the permittivity. An analysis of the dispersion parameters in a wide temperature range has demonstrated that it can be due to the relaxation of domain walls in PMN + 2 wt % Li₂O that appear most likely because of the existence of anomalously coarse grains in PMN + 2 wt % Li₂O.     

Vibrational spectrum of Li2B4O7 crystals

The polarized infrared reflection spectra of Li₂B₄O₇ were studied in the spectral range 80–1600 cm^?1 and compared with Raman spectra. From the spectrum dispersion analysis, the frequencies, damping, and dielectric oscillator strengths were determined for all vibrational modes observed. A calculation of the effective charges and an analysis of the chemical-bond types of the Li₂B₄O₇ crystal structural units were carried out on the basis of the obtained data.     

Change of the oxidation state of phosphorus in sputtered Li3±xPO4±y and Li3±xPO4±yNz films

Thin Li_3±xPO_4±yN_zLi⁺- electrolyte films prepared by reactive rf-magnetron sputtering of Li₃PO₄ incorporate a certain amount of nitrogen which is made responsible for increased Li⁺-conductivity as well as at least kinetic stability with lithium metal. A possible change of the oxidation state +5 of phosphorus as a result of the sputter process has not yet been considered for explanation. We have found out that it cannot be generally assumed that reactive low power rf-magnetron sputtering of Li₃PO₄ results in fully oxidized films, even when pure O₂ is employed as sputtering gas. Our films immediately react with H₂O releasing a garlic smelling gas. The reaction area is surrounded by a white crust afterwards. CuSO₄ and AgNO₃ aqueous solutions become reduced. Impedance measurements yield an ionic conductivity of 2·10⁻⁶ S/cm at 25 °C and an activation energy of 0.62 eV.