Piercarlo Mustarelli

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.

Effects of water-soluble functionalized multi-walled carbon nanotubes examined by different cytotoxicity methods in human astrocyte D384 and lung A549 cells

The widespread projected use of functionalized carbon nanotubes (CNTs) makes it important to understand their potential harmful effects. Two cell culture systems, human A549 pneumocytes and D384 astrocytoma cells, were used to assess cytotoxicity of multi-walled CNTs (MWCNTs) with varying degrees of functionalization. Laboratory-made highly functionalized hf-MW-NH(2) and less functionalized CNTs (MW-COOH and MW-NH(2)) were tested in comparison with pristine MWCNTs, carbon black (CB) and silica (SiO(2)) by MTT assay and calcein/propidium iodide (PI) staining. Purity and physicochemical properties of the test nanomaterials were also determined. In both MTT and calcein/PI assays, highly functionalized CNTs (hf-MW-NH(2)) caused moderate loss of cell viability at doses >or=100 microg/ml being apparently less cytotoxic than SiO(2). In preparations treated with CB or the other nanotube types (pristine MWCNTs, MW-COOH and the less functionalized amino-substituted MW-NH(2)) the calcein/PI test indicated no loss of cell viability, whereas MTT assay apparently showed apparent cytotoxic response, occurring not dose-dependently at exceedingly low CNT concentrations (1 microg/ml). The latter nanomaterials were difficult to disperse showing higher aggregate ranges and tendency to agglomerate in bundle-like form in cell cultures. In contrast, hf-MW-NH(2) were water soluble and easily dispersible in medium; they presented lower aggregate size range as well as considerably lower length to diameter ratios and low tendency to form aggregates compared to the other CNTs tested. The MTT data may reflect a false positive cytotoxicity signal possibly due to non-specific CNT interaction with cell culture components. Thus, these properties obtained by chemical functionalization, such as water solubility, high dispersibility and low agglomeration tendency were relevant factors in modulating cytotoxicity. This study indicates that properties obtained by chemical functionalization, such as water solubility, high dispersibility and low agglomeration tendency are relevant factors in modulating cytotoxicity of CNTs.

Structure and transport properties of polymer gel electrolytes based on PVdf-HFP and LiN(C2F5SO2)2

Abstract Gel polymer electrolytes composed of PVdF/HFP and a non-aqueous lithium electrolyte solution EC/DEC/LiN(C 2 F 5 SO 2 ) 2 (BETI) were prepared to investigate the conduction properties of the gel materials. Structural and micro-structural characterization was carried out by means of modulated differential scanning calorimetry (MDSC) and scanning electron microscopy (SEM). The samples with polymer/solution weight ratios higher than 0.5 contain at least an amorphous swollen gel phase and a crystalline one, while a pure liquid phase appears, which occupies cavities in the micrometer range in the gels with lower polymer content. The transport properties of the gels were investigated by means of impedance spectroscopy for conductivity and pulsed-field gradient nuclear magnetic resonance (PFG-NMR) for diffusion coefficients. The results were compared with those of corresponding films prepared with LiN(CF 3 SO 2 ) 2 (TFSI). The BETI-based samples showed diffusion values lower than the TFSI-based ones. Estimation of the carrier concentration change with the gel composition revealed that the interaction between the host polymer and the electrolyte in the gel especially in the polymer rich region (>50 wt%).

Polymer fuel cells based on polybenzimidazole/H3PO4

Polybenzimidazole-based membranes are nowadays considered the best alternative to Nafion® for the fabrication of high-temperature polymer fuel cells. The rich chemistry of benzimidazole allows us to widely change the physicochemical properties of the resulting polymers and, consequently, to tune the functional properties of the electrolyte membrane. In this perspective we report the most recent developments in PBI-based membranes, cells and stacks. Emphasis is given to problems such as acid leaching, membrane degradation and stack durability.

Transport properties and microstructure of gel polymer electrolytes

Abstract Gel polymer electrolytes based on a copolymer poly(vinylidene fluoride (VdF)/hexafluoropropylene (HFP)) and a solution of ethylene carbonate (EC), diethyl carbonate (DEC) and as a salt LiN(CF 3 SO 2 ) 2 were prepared by changing the content of the polymer in the range 20–80 wt%. The effects of changing the salt concentration in the solution were also explored. The conductivity was found to vary in the range 10 −2 ohm −1 cm −1 (20 wt% of polymer) to 10 −8 ohm −1 cm −1 (80 wt% of polymer). Pulsed field gradient (PFG)-NMR was used to determine the diffusion coefficient of lithium ( D Li + )and fluoride species ( D F − )and in consequence the transport number. Both D Li + and D F − decrease with increasing polymer content. Cation transport number ( τ + ) values between 0.49 and 0.60 were found, depending on the solution content. Pores having average diameter of about 0.5 μm were observed by scanning electron microscopy (SEM).

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.

Li+ solvation in ethylene carbonate–propylene carbonate concentrated solutions: A comprehensive model

Spectroscopic (Raman, NMR, impedance spectroscopy), and thermal [differential scanning calorimetry (DSC)] techniques have been used to study the solvation mechanism of lithium ions in ethylene carbonate (EC)–propylene carbonate (PC) concentrated solutions. For values of N=[Li+]/[EC+PC]⩽0.2 all the cations are solvated by ∼4 solvent molecules and interaction chiefly takes place between Li+ and the ring oxygens. For N>0.2 a part of Li+ ions begins to form complexes with two solvent molecules (sandwich configuration). At N≅0.5 nearly all cations are complexed, and a crystalline compound is formed at room temperature. For higher values of N a reassociation of the salt takes place.

7Li and 19F diffusion coefficients and thermal properties of non-aqueous electrolyte solutions for rechargeable lithium batteries

Abstract In this paper, electrolyte solutions of ethylene carbonate (EC) and ethylene methylene carbonate (EMC) with different salts as LiPF6, LiBF4 and LiN(SO2C2F5)2 were prepared and characterized using Pulsed Field Gradient (PFG) NMR and DSC. Cation transport numbers, τ+, ranging between 0.37 and 0.49 were obtained. The maximum value of 0.49 was obtained in the case of a 0.5 M solution of LiBF4 in 2:8 EC:EMC. The DSC data suggest that the increase of EMC stabilizes the electrolyte solution towards low temperature, and that a 2:8 EC:EMC ratio assures good stability at low temperature to the electrolyte solution. While LiN(SO2C2F5)2 seems to score the best in terms of low temperature stability, LiPF6 may offer the best cost/performances compromise.

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.

Innovative high performing metal organic framework (MOF)-laden nanocomposite polymer electrolytes for all-solid-state lithium batteries

An enhancement of two orders of magnitude in the ambient temperature ionic conductivity of poly(ethylene oxide)-based nanocomposite polymer electrolyte (NCPE) membranes is here fundamentally achieved by the incorporation of specific amounts of aluminium-based metal organic framework (MOF) as the filler. Thorough characterization, particularly solid-state NMR and FT-IR studies, shed light on the specific role of the defective MOF frameworks in greatly enhancing the Li+ ion mobility inside the polymeric matrix. The prepared NCPEs are highly stable towards lithium metal even after prolonged storage time, and an excellent cycling profile is evidenced even at moderate temperatures, which has never been reported so far for an all-solid-state lithium polymer cell composed of Li/NCPE/LiFePO4.