Physical and optical properties of Li2O-MgO-B2O3 doped with Dy3+

The study on the optical properties of alkali borate glasses doped with rare earths is an interesting area of research. Dysporosium doped lithium magnesium borate glasses were prepared by melt-quenching technique with dysporosium concentration varying from 0.3 to 1.0 mol %. Physical and optical properties of Lithium Magnesium Borate doped with different concentration of Dy³⁺ were observed based on its physical parameters, emission spectra and absorption spectra. The absorption spectra of this study exhibits eight absorption bands with hypersensitive peak at 1260 nm (⁶ H _9/2). Two emitted spectra transitions were also observed at ⁴ F _9/2 → ⁶ H _15/2, ⁴ F _9/2 → ⁶ H _13/2. Lastly, important physical parameters for each concentration of dopant such as density, ions concentration, polaron radius, inter-nuclear distance, refractive index, oscillator strength and other parameters were determined.     

Investigation of the boron-oxygen network in borate glasses by infrared spectroscopy

Lithium borate glasses are fast ionic conductors in which the lithium ions conductivity is all the more important as the content in lithium oxide and in lithium salt is higher. In the perspective of their use as electrolytes in solid state micro-batteries, we have studied the conformation of the boron-oxygen network of lithium halides “doped” glasses by MIR spectroscopy. The modifying properties of the lithium oxide on the binary system B₂O₃-Li₂O are investigated by the same technique and the results are used to understand the modifications of the boron-oxygen network induced by the “doping salt”. The observed results depend on the type of salt anions: fluoride anions participate directly to the O/B network while chloride and bromide anions are in interstitial position in the glass matrix.     

The effect of europium oxide impurity on the optical and physical properties of lithium potassium borate glass

The most hosts that is utilized in scientific application is borate glass. By using melt-quenching technique, five samples of lithium potassium borate (LKB) doped with different concentration of europium oxide (Eu₂O₃) were prepared. To investigate the influence of dopant on the optical and physical characteristics of the proposed glass, two methods have been applied (XRD, PL). The amorphous nature was confirmed by X-ray diffraction (XRD). The physical parameters of the glass matrix doped by different oxidation state have been analyzed, these parameters are density, molar volume, ion concentration, inter-nuclear distance, and polaron radius. The exchange in the concentration of Eu³⁺ indicated the influence of Eu as a dopant on the photoluminescence (PL) emission of LKB glasses. The emission spectrum of LKB:Eu³⁺ show a chain of emission bands, which are attributed to ⁵ D ₀-⁷ F _r (r = 1–4) transition of Eu³⁺. The luminescence studies showed four peaks 590 (yellow), 613 (orange), 650 (red), and 698 nm (red) for all samples except sample 0, the high luminescence efficiency is in emitting orange light at 613 nm.     

High performance PEO-based polymer electrolytes and their application in rechargeable lithium polymer batteries

Solvent-free, lithium-ion-conducting, composite polymer electrolytes have been prepared by a double dispersion of an anion trapping compound, i.e., calyx(6)pyrrole, CP and a ceramic filler, i.e., super acid zirconia, S-ZrO₂ in a poly(ethylene oxide)-lithium bis(oxalate) borate, PEO–LiBOB matrix. The characterization, based on differential thermal analysis and electrochemical analysis, showed that while the addition of the S-ZrO₂ has scarce influence on the transport properties of the composite electrolyte, the unique combination of the anion-trapping compound, CP, with the large anion lithium salt, LiBOB, greatly enhances the value of the lithium transference number without depressing the overall ionic conductivity. These unique properties make polymer electrolytes, such as PEO₂₀LiBOB(CP)_0.125, of practical interest, as in fact confirmed by tests carried out on lithium battery prototypes.     

MgAl2SiO6-incorporated poly(ethylene oxide)-based electrolytes for all-solid-state lithium batteries

Poly(ethylene oxide) (PEO)-based composite polymer electrolytes (CPEs), comprising various concentrations of lithium hexafluorophosphate and magnesium aluminium silicate, were prepared by hot-press technique. The membranes were characterised by scanning electron microscopy, tensile and thermal analyses. It has been demonstrated that the incorporation of the ceramic filler in the polymeric matrix has significantly enhanced the ionic conductivity, thermal stability and mechanical integrity of the membrane. It also improved the interfacial properties with lithium electrode. Finally, an all-solid-state lithium cell composed of Li/CPE/LiFePO₄ has been assembled and its cycling performance was analysed at 70 °C. The cell delivered a discharge capacity of 115 mAh g^?1 at 1 °C rate and is found to be higher than previous reports.     

Characterization of PEO/PVP/GO nanocomposite solid polymer electrolyte membranes: microstructural,thermo-mechanical,and conductivity properties

Poly (ethylene oxide) (PEO)/polyvinylpyrrolidone (PVP) blended nanocomposite polymers, incorporating graphene oxide (GO) nano-sheets and embedded with NaIO₄ salt, were prepared using solution casting technique. The as-prepared nanocomposite electrolyte membranes were characterized by SEM, TEM, XRD, and Raman vibrational spectroscopic techniques to confirm the dispersion of GO nano-sheets and to understand the synergistic properties of GO/polymer interactions as a function of GO nano-sheets concentration. GO fillers incorporated electrolyte membranes demonstrated distinctive surface morphology composed of circular-shaped protuberances of different dimensions. The decrease of Raman intensity ratio (I_D/I_G) and in-plane crystallite size (L_a) values of the nanocomposites suggested the good dispersion and confinement of the GO nano-sheets. The optical properties of blend electrolyte films were studied as a function of GO filler concentration using optical absorption and diffuse reflectance spectra. In reference to PEO/PVP/NaIO₄, the resultant PEO/PVP/NaIO₄/GO (0.4% in weight) electrolyte membrane demonstrated both an increase in tensile strength of ca. 42% and in Young’s modulus of ca. 40%, improvements coupled with a maximum fractured elongation of 3%. Through impedance spectroscopy analysis, the role of the GO nano-sheets onto the room temperature conductivity properties of the prepared electrolyte membranes has been probed.     

LiFAP-based PVdF–HFP microporous membranes by phase-inversion technique with Li/LiFePO<Subscript>4</Subscript> cell

Polyvinylidenefluoride–hexafluoropropylene-based (PVdF–HFP-based) gel and composite microporous membranes (GPMs and CPMs) were prepared by phase-inversion technique in the presence 10 wt% of AlO(OH) _n nanoparticles. The prepared membranes were gelled with 0.5-M LiPF₃(CF₂CF₃)₃ (lithium fluoroalkylphosphate, LiFAP) in EC:DEC (1:1 v/v) and subjected to various characterizations; the AC impedance study shows that CPMs exhibit higher conductivity than GPMs. Mechanical stability measurements on these systems reveal that CPMs exhibit Young’s modulus higher than that of bare and GPMs and addition of nanoparticles drastically improves the elongation break was also noted. Transition of the host from α to β phase after the loading of nanosized filler was confirmed by XRD and Raman studies. Physico-chemical properties, like liquid uptake, porosity, surface area, and activation energy, of the membranes were calculated and results are summarized. Cycling performance of Li/CPM/LiFePO₄ coin cell was fabricated and evaluated at C/10 rate and delivered a discharge capacity of 157 and 148 mAh g⁻¹ respectively for first and tenth cycles.     

Ionic-electronic mixed conduction in LixV2O5

The dc conductivity of lithium vanadium bronze, Li_xV₂O₅ was measured on polycrystal prepared by solid-state reaction in the x region 0.25–0.70. Both electronic and ionic conduction was observed. The former increased with increase of lithium content and was nearly equal to the total conductivity 10^-1–10⁰ S/cm. The ionic conductivity (∽10^-4 S/cm) measured by dc four-probe technique decreased as the lithium content increased in the range 400–500°C. The apparent activation energy for ionic conduction varied from 57 kJ/mol for x of 0.25 to 82 kJ/mol for x of 0.50.     

Ion dynamics in methylcellulose–LiBOB solid polymer electrolytes

A polymer electrolyte system comprising methylcellulose (MC) as the host polymer and lithium bis(oxalato) borate (LiBOB) as the lithium ion source has been prepared via the solution cast technique. The electrolyte with the highest conductivity of 2.79 μS cm^?1 has a composition of 75 wt% MC–25 wt% LiBOB. The mobile ion concentration (n) in this sample was estimated to be 5.70?×?10²⁰ cm^?3. A good correlation between ionic conductivity, dielectric constant, and free ion concentration has been observed. The ratio of mobile ion number density (n) at a particular temperature to the concentration n ₀ of free ions at T?=?∞ (n/n ₀) and the power law exponents (s) exhibit opposite trends when varied with salt concentration.     

The first synthesis of a graphite bis(oxalato)borate intercalation compound

A new graphite intercalation compound containing the bis(oxalato)borate anion, B[OC(O)C(O)O]₂⁻, is prepared for the first time by chemical oxidation of graphite with fluorine gas in the presence of a solution containing the intercalate anion in anhydrous hydrofluoric acid. The products of stage 1-3 compounds are characterized by powder X-ray diffraction, thermogravimetric analysis, and elemental analyses. X-ray diffraction data indicate a standing-up orientation for the borate anion, with long axis perpendicular to the graphene sheets. Elemental analyses provide x and δ for the nominal composition of C_xB[OC(O)C(O)O]₂·δF, where the chelate borate and fluoride are co-intercalates, and indicate a low borate, and high fluoride, intercalate content as compared to anion packing in other graphite intercalation compounds.     

Electrochemical and mechanical properties of nanochitin-incorporated PVDF-HFP-based polymer electrolytes for lithium batteries

Nanocomposite polymer electrolytes (NCPE) composed of poly(vinylidenefluoride-co-hexafluoropropylene) (PVDF-HFP) and chitin for different concentrations of LiClO₄ have been prepared by a hot-press technique. The prepared NCPE films were subjected to XRD, SEM, FTIR and tensile analyses. The thermal stability of NCPE membrane was investigated by TG-DTA. Ionic conductivity studies have also been made as a function of lithium salt concentration for different temperatures ranging from 0 to 80 °C. The polymeric membrane comprising PVDF-HFP/chitin/LiClO₄ of ratio 75:20:5 (wt.%) offered maximum ionic conductivity. Thermal study reveals that these membranes are stable up to 260 °C.     

Synthesis and characterization of thermoluminescent Li2B4O7 nanophosphor

Lithium borate (Li₂B₄O₇) is a low Z_eff, tissue equivalent material that is commonly used for medical dosimetry using the thermoluminescence (TL) technique. Nanocrystals of lithium borate were synthesized by the combustion method for the first time in the laboratory. TL characteristics of the synthesized material were studied and compared with those of commercially available microcrystalline Li₂B₄O₇. The optimum pre-irradiation annealing condition was found to be 300 °C for 10 min and that of post-irradiation annealing was 300 °C for 30 min. The synthesized Li₂B₄O₇ nanophosphor has very poor sensitivity for low doses of gamma up to 10¹ Gy whereas from 10¹ to 4.5×10² Gy this phosphor exhibits a linear response and then from 4.5×10² to 10³ Gy it shows supralinearity. Thermoluminescence properties of Li₂B₄O₇ nanophosphor doped with Cu has also been investigated in this paper. It shows low fading and a linear response over a wide range of gamma radiation from 1×10² to 5×10³ Gy. Therefore the synthesized lithium borate nanophosphor doped with Cu may be used for high dose measurements of gamma radiations.     

The Effect of TiO2 and MgO on the Thermoluminescence Properties of a Lithium Potassium Borate Glass System

The influence of dopant TiO₂ and co-dopant MgO on the thermoluminescence (TL) properties of lithium potassium borate glass (LKB) is reported in this paper. The glow curve exhibits a prominent peak (T_m) at 230 °C. The TL intensity was enhanced by a factor of ~3 due to the incorporation of MgO, and this was attributed to the creation of extra electron traps mediated by radiative recombination energy transfer. We achieved good linearity of the TL yield with dose, low fading, excellent reproducibility and a promising effective atomic number (Z_eff=8.89), all of which are highly suitable for dosimetry. The effect of heating rate, sunlight and dose rate on the TL are also examined. These attractive features demonstrate that our dosimeter is useful in medical radiation therapy.     

PVdF-HFP membranes for fuel cell applications: effects of doping agents and coating on the membrane’s properties

Poly(vinylidene fluoride-co-hexafluoropropene)–hexafluoropropylene (PVdF-HFP; M _n, 130,000)-based membranes were prepared by means of phase inversion technique by coagulating with water and MeOH and then doping with H₃PO₄ and H₂SO₄. In order to improve the electrochemical properties of the PVdF-HFP membranes, coagulated membranes were also coated with polystyrene-block-poly(ethylene-ran-butylene)-block-polystyrene (PSEBS) and sulfonated with chlorosulfonic acid in the second stage. The effects of the type of coagulant, coagulation time, doping agents, coating, and sulfonation on the membrane properties were investigated. Membranes were thermally stable up to 400 °C. The conductivity values were measured to be between 1.10E???01 and 6.00E???03 mS/cm for uncoated samples. The proton conductivity value of the PSEBS-coated and sulfonated membrane was increased from 6.00E???03 to 92.1 mS/cm. Water uptake values varied from 0 to 38 % for uncoated samples and from 11.5 to 65.2 % for coated samples. Chemical degradation of PVdF-HFP membranes was investigated via Fenton test. All membranes were found to be chemically stable. Morphology of the membranes was examined by scanning electron microscopy. Different membrane morphologies were observed, depending on different membrane preparation procedures.     

Effect of copper addition on BO<Subscript>4</Subscript>, H<Subscript>2</Subscript>O groups and optical properties of lithium lead borate glass

Lead lithium borate glass samples composition 50Li₂B₄O₇–(50?x)Pb₃O₄–x CuO, where x = 0–35 mol% were prepared by melt quenching method. The density of the prepared samples was measured and molar volume was calculated. IR spectra were measured for the prepared samples at room temperature to investigate the glass structure. The IR spectra were deconvoluted using curves of Gaussian shape at approximately the same frequencies. The deconvoluted data were used to study the effect of CuO content on all the structural borate and water groups. The optical band gap obtained directly from absorption coefficient, refractive index and extinction coefficient, also by using the Tauc model. The type of transition is determined by the simple and accurate method.     

Montmorillonite-based ceramic membranes as novel lithium-ion battery separators

Novel montmorillonite-based ceramic membrane (CM) has been prepared with poly(vinylidene fluoride-co-hexafluoropropene) (PVdF-HFP) copolymer as binder. Physical properties such as surface morphology, porosity, liquid electrolyte uptake and thermal stability were analysed. The ceramic membrane was activated by soaking it in a non-aqueous liquid electrolyte (1.0 M LiPF₆ solution in 1/1 v/v ethylene carbonate/diethyl carbonate mixture) for 10 min. The compatibility of the membrane with lithium metal anode as a function of storage time was analysed by assembling a Li/CM/Li symmetric cell. Finally, a lab-scale cell composed of Li/CM/LiFePO₄ is assembled and its cycling performance analysed at different C-rates. Although the ceramic membrane is not flexible, it shows high thermal stability and stable interfacial properties when in contact with the lithium metal anode. A stable cycling behaviour is demonstrated even at 1C-rate with limited fade in capacity.     

A study on LiBOB-based nanocomposite gel polymer electrolytes (NCGPE) for Lithium-ion batteries

Lithium bis(oxalato)borate (LiBOB) salt-based nanocomposite gel polymer blend electrolyte (PVdF/PVC) membranes have been prepared by solution casting technique for various concentrations of TiO₂. The effect of anatase structure of nanosized titanium dioxide in the plasticized PVC/PVdF + LiBOB matrix has been observed in the 2:1 salt filler ratio in the impedance measurements that the conductivity is increased one order of magnitude higher than the filler-free electrolyte (1:0 salt:filler ratio). The phase morphology of this electrolyte membrane represents the appearance of the free volume sites for ionic migration.     

Investigation of structural properties of lead strontium borate glasses for gamma-ray shielding applications

Glasses of the system PbO-SrO-B₂O₃ with the value of molar ratio R (=PbO/B₂O₃) in the region 0.14≤R≤2.0 were prepared using the melt quenching technique. In order to evaluate gamma-ray shielding properties for glass samples, mass attenuation coefficients have been calculated with the XCOM computer program. The longitudinal velocities of ultrasonic waves were measured in these glass samples at room temperature using the pulse echo technique. The results indicate that with increase in R value, stability of glass network decreases. Stability of glass network decreases indicate the increase in the number of borons with non-bridging oxygens at the expense of decrease of tetrahedral borate units. This feature may lead to open glass structure with lesser rigidity of the glass samples. DSC studies have been undertaken to measure the glass transition temperature and to get an idea about stability of the glass network with increasing R value.     

Blends of hexanoyl chitosan/epoxidized natural rubber doped with EMImTFSI

Hexanoyl chitosan soluble in THF is prepared by acyl modification of chitosan. Epoxidation natural rubber (ENR25) (25 mol%) is chosen to blend with hexanoyl chitosan. Films of hexanoyl chitosan/ENR25 blends containing lithium bis(trifluoromethanesulfonyl)imide (LiN(CF₃SO₂)₂) and 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EMImTFSI) are prepared by solution casting technique. FTIR results suggested that LiN(CF₃SO₂)₂ salt interacted with hexanoyl chitosan, ENR25, and EMImTFSI. EMImTFSI interacted with hexanoyl chitosan and ENR25 to form EMIm⁺-hexanoyl chitosan and EMIm⁺-ENR25 complexes, respectively. The effect of EMImTFSI on the morphology and thermal properties of the blends is investigated by polarized optical microscopy (POM) and differential scanning calorimetry (DSC), respectively. The ionic conductivity of the electrolytes is measured by electrochemical impedance spectroscopy (EIS). Upon addition of 12 wt% EMImTFSI, a maximum conductivity of 1.3 × 10^?6 S cm^?1 is achieved. Methods based on impedance spectroscopy and FTIR are employed to study the transport properties of the prepared polymer electrolytes. The ac conductivity was found to obey universal law, σ(ω)?=?σ _dc ?+?Aω ^S . The temperature dependence of exponent s is interpreted by the small polaron hopping (SPH) model.     

Effect of nanochitosan on electrochemical, interfacial and thermal properties of composite solid polymer electrolytes

PEO-based solid polymer electrolyte films with various concentrations of nanochitosan as filler and LiCF₃SO₃ as salt were prepared by membrane hot-press technique. Nanochitosan was prepared from chitosan by conventional chemical cure method. The prepared composite membranes were characterized by FT-IR, XRD, thermal, SEM, AFM analyses, electrochemical impedance spectroscopy, cyclic voltammetry and compatibility studies. The ionic conductivity and thermal stability of the polymer membranes were enhanced significantly by addition of nanofiller. The compatibility studies reveal that filler incorporated membrane is better compatible with lithium interface than filler free electrolyte.