In this work we address the phenomena at the basis of the performance loss in a Li-O cell operating in the presence of a lithium bis(trifluoromethanesulfonyl)imide (LiTFSI)/tetraethylene glycol dimethyl ether (TEGDME) salt/solvent couple and a porous carbonaceous cathode. The cell was discharged/charged applying both voltage and capacity limits, and the effects of repeated galvanostatic cycling were addressed. The ex situ characterization of carbonaceous cathodes corresponding to different cutoff voltages was based on vibrational spectroscopies, transmission electron microscopy, and X-ray photoelectron spectroscopy. The reversible precipitation/decomposition of undesired products deriving from degradation of both carbon cathode and ethereal solvent is pointed out within a single voltage limited (2.0-4.6 V) discharge/charge cycle, whereas their irreversible accumulation on the surface of the electrode results after 100 capacity limited cycles. At the same time, the presence of polar degradation products (carbonates and carboxylates) at the cathode surface is accompanied by the buildup of a surface electric potential gradient, as revealed by differential binding energy shifts resulting from C 1s photoelectron spectra. This effect, seldom reported for Li-ion batteries, is for the first time put in evidence for a Li-O cell. Furthermore, the use of TFSI anion is shown to lead to carbonate-based degradation products not involving the formation of LiCO. The peculiar occurrence of such degradation phenomena are attributed to the intrinsic low-donor number characteristic of the TFSI anion.
Integration of graphene on flexible and transparent supports, such as ITO/PET, represents a challenging goal for the realization of next-generation optoelectronic materials. In this context, reduced graphene oxide (rGO) results an elective material for its easy handling and wide range of possibilities for processing. We present two different synthetic routes to prepare an interface between rGO and ITO/PET by an electrochemical approach: a direct electrodeposition of rGO onto the ITO/PET support by reduction of GO monolayers suspended in water (one-step approach) and the reduction of bulk GO films previously deposited onto the ITO/PET support (two-step approach). XPS analysis revealed that in both cases rGO is formed onto the surface of ITO/PET, successfully leading to a flexible rGO/ITO/PET interface. The one-step method proved more direct and simpler, though with less discernible electrochemical features. Instead, the two-step approach provided clearly detectable electrochemical signals, which enable a more facile tuning of the reduction parameters.
In this work we discuss the co-catalysis in aprotic Li-O 2 batteries of C-free nanostructured mixed oxide electrodes decorated by Pd/PdO core/shell nanoparticles. A Cr(III) doped NiCo 2 O 4 material has been grown hydrothermally on an open Ni-mesh. Palladium nanoparticles have been synthesized by pulsed lased ablation in liquid acetone in the fs regime and deposited by drop casting onto the surface of the nanostructured mixed oxide electrodes. The resulting electrodes have been calcined at 300 • C. The use of laser techniques to produce nanoparticles for aLOBs is here proposed for the first time in the literature, as well as the peculiar combination of Pd/PdO nanoparticles deposited onto C-free Cr(III) doped NiCo 2 O 4 self-standing electrodes. Performance in aprotic Li-O 2 batteries have been recorded in galvanostatic conditions and post mortem analysis of the electrode surfaces have been carried out by X-ray photoemission spectroscopy. The use of Pd/PdO nanoparticles as co-catalysts enhances the reversibility of the electrochemical oxygen reduction/evolution reactions. This beneficial effect originates by the decrease of the mean overvoltages compared to the bare Cr(III) doped NiCo 2 O 4 electrodes, and extends the cell calendar life from 16 to 41 fully reversible galvanostatic cycles at J = 0.2 mAcm −2 with capacity limitation of 0.2 mAhcm −2 .
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