Aldo Magistris

Effects of nanoscale SiO2 on the thermal and transport properties of solvent-free, poly(ethylene oxide) (PEO)-based polymer electrolytes

Solvent-free, composite electrolytes based on poly(ethylene oxide) (PEO) have been prepared by using LiClO4 and LiN(CF3SO2)2 as the doping salts, and nanoscale SiO2 as the filler. The samples have been characterized for what concerns their thermal and transport properties. The addition of the filler determines an increase of the conductivity of more than one order-of-magnitude, depending on the filler concentration. The maximum value of 1.4×10−4 ohm−1 cm−1 is obtained for the sample PEO8–LiN(CF3SO2)2–5 wt% SiO2. Effects of the silica thermal history on the conductivity level have been also ascertained. The cation transport number, t+, changes from ~0.1 to ~0.2 when 10 wt% of filler is added.

Silver borophosphate glasses : Ion transport, thermal stability and electrochemical behaviour

Abstract An experimental study of the undoped and AgI-doped borophosphate glasses is presented which includes discussion of the glass forming properties, thermal and redox stability, ionic conductivities and transport numbers for the “quaternary” system AgI : Ag 2 O : B 2 O 3 : P 2 O 5 . For glasses without AgI and with the same Ag 2 O molar fraction, the conductivity at room temperature (rt) may be a highly non-linear function of the B/P ratio. By appropriately mixing boron and phosphorus oxides, undoped glasses can be obtained with better rt conductivities and thermal stability than corresponding glasses made with a single glass former (mixed anion effect). The electrochemical behaviour of several undoped and AgI doped glasses has been characterized by triangular voltammetry techniques.

Short range order and glass transition in AgIAg2OB2O3 vitreous electrolytes

Abstract Several experimental techniques are used to study the short range order, the dynamics and the glass transition in AgIAg2B2O3 compounds. Addition of Ag2O to B2O3, up to [Ag2O]/[B2O3] ⩽0.5 modifies the borate network by creating a BO4 unit for each silver added. Addition of AgI decreases the glass transition temperature (Tg) but has only minor effects on the short range structure of the borate network. Silver iodide is partially accomodated in the interstices of the glass network. The relationship among a tentative structural picture, the ion transport phenomena and the low temperature dynamics are discussed. An investigation of the dynamics in the AgI·Ag2O·2B2O3 glass near and above Tg is presented. With NMR techniques, we monitor the onset of tumbling of the borate units and the dynamical effects of crystallization and/or aging of the glass. Hysteresis effects in the ionic conductivity (σ) temperature dependence and the non-Arrhenian behavior of σT near Tg are interpreted in terms of structural modifications occurring at elevated temperatures in the glass.

Lithium borophosphate vitreous electrolytes

Abstract This paper investigates the ionic (Li+) conductivity and thermal stability properties of glasses of the Li2O/B2O3/P2 O5 system. For the same molar ratio between lithium oxide and glass formers (B2O3 + P2O5), the ionic conductivities at room temperature can be substantially higher in borophosphate glasses than in pure borates or phosphates. An attempt is made to relate this technologically interesting conductivity enhancement to the coordination chemistry of borophosphate glasses.

PVDF-based porous polymer electrolytes for lithium batteries

Abstract Gel electrolytes based on PVDF and PVDF-HFP membranes with different morphology and porosity have been prepared by means of the phase inversion technique. Diffusion coefficients and conductivity have been measured in order to investigate the role of the morphology and microstructure on the dynamics and ionic transport of these multi-phase gels. The picture emerges of a two-steps gelation process, in which the majority of the solution fills up the cavities, while a non-negligible fraction of the salt–solvent mixture swells the amorphous strands of the polymer. Pure PVDF porous membranes display one or two diffusion coefficients, depending on the level of porosity and the film morphology. The two components are attributed respectively (1) to the carriers in the swollen phase and (2) to the pure solution, whose motion can be “free” or, in such cases, partially restricted by the barriers of the cavities. A single component can be interpreted as a sort of average between the pure solution and the swollen phase. PVDF-HFP membranes generally present two diffusion coefficients and show an opposite behaviour between the cation and anion species, concerning their relative amounts.

Formation of high conductivity glasses in the system AgIAg2OB2O3

Glass phases showing high ionic conductivity at room temperature were prepared through a rapid quenching of the molten mixtures of the system AgIAg2OB2O3 (a fixed Ag2O/B2O3 = 1 molar ratio was always considered): the obtained specimens were homogeneous and transparent cylindrical blocks. Disk shaped cells prepared with such specimens did not show any grain-grain effect as supported by the comparison between four electrodes dc and ac conductivity determinations. A less than 10−9(ohm cm)−1 electronic conductivity was found. According to X-rays diffraction and DTA investigations, XAgI > 0.8 samples contained crystallized AgI, whereas 0.1 < XAgI < 0.8 samples could be considered actual vitreous homogeneous phases. AgI contents lower than 10 mole% were not considered due to the observed presence of segregated metallic silver. Room temperature density and conductivity data showed a regular behaviour vs XAgI in the vitreous phases range, whereas an evident discontinuity was observed about XAgI = 0.8. Linear fits in the Arrhenius plots of the bulk conductivity were obtained in the 120 K−Tg (glass transition temperature) range: the corresponding activation energies, as well as the high room temperature conductivities, allowed to closely compare these vetrous phases with the so called “superionic” conductors.

Investigations by impedance spectroscopy on the behaviour of poly(N,N-dimethylpropargylamine) as humidity sensor

Abstract A thin film of poly( N , N -dimethylpropargylamine) (PDMPA), deposited by spin coating over a SiO 2 substrate covered by an interdigitated array of chromium electrodes, was characterised by impedance spectroscopy at different relative humidity levels, ranging from ∼0 to ∼90% relative humidity (RH). The logarithm of the film conductance exhibits a linear behaviour from very low RH contents up to more than 70% RH. The dynamic range of the variation of the conductance is extremely high (∼6 orders-of-magnitude) and it allows a promising use of the film as a humidity sensor.

Poly(ethylene oxide) Complexes of Lead Halides New Polymeric Conductors of Pb2

Poly(ethylene oxide) (PEO) easily forms complexes with PbBr/sub 2/, PbI/sub 2/, and PbCl/sub 2/. Compositions over the range of PbBr/sub 2/ . (PEO)/sub 8-30/, PbI/sub 2/ . (PEO)/sub 6-40/, and PbCl/sub 2/ . (PEO)/sub 16/ have been prepared by a two-solvent technique in which PEO is dissolved in acetonitrile and the salt is dissolved in dimethylsulfoxide. The lead halide complexes are stable to nearly 300/sup 0/C and are quite conductive. PbBr/sub 2/ . (PEO)/sub 8/, for example, has an ionic conductivity of 10/sup -6/-10/sup -7/ (..cap omega..-cm)/sup -1/ at 180/sup 0/C and in the range of 10/sup -5/ (..cap omega..-cm)/sup -1/ at 250/sup 0/C. Preliminary transport number measurements have shown that PbBr/sub 2/ . (PEO)/sub 20/ is a reasonably good conductor of Pb/sup 2+/.

Ion transport and thermal properties of poly(ethylene oxide) - LiClO4 polymer electrolytes

Abstract The ion transport and thermal properties of polymer electrolytes formed by poly(ethylene oxide) (PEO) and lithium perchlorate are discussed. The phase diagram is examined over a LiC1O 4 concentration range of 0 – 34 mole %: regions of existence of amorphous and crystalline phases are defined. Conductivity and activation energies of the polymers have been determined through complex impedance analysis of cells with blocking electrodes. For the amorphous 8:I composition, which exhibits the highest ionic conductivity, the lithium transport number, measured at 70 – 150 °C using reversible Li electrodes, is approximately constant and equal to 0.30.

Transport and thermal properties of (PEO)n–LiPF6 electrolytes for super-ambient applications

Abstract Poly(ethylene oxide) (PEO)-based solvent-free electrolytes may be used for applications above room temperature, e.g. in batteries for electric vehicles. The system PEO–LiPF 6 has to date received only scarce attention because of the poor thermal stability and hygroscopicity of the lithium salt. However, for applications above the melting of PEO crystalline phase, it is possible to consider films with relatively low salt content, which can overcome the above-mentioned problem. In this paper, we perform a thermal and transport characterisation of the system PEO–LiPF 6 . We show that conductivity values above 10 −4 Ω −1 cm −1 can be reached at 70°C for n =EO/Li=30. The addition of nanoscale silica is shown to influence the thermal decomposition of the salt.