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We examine the formation of the solid electrolyte interface (SEI) on anodes made of carbon encapsulated zinc ferrite (ZnFe2O4) nanoparticles (50 nm ZFO-C) as a standard metal oxide electrode prototype. The SEI formation and phase evolution are studied by two soft X-ray absorption techniques with different probing depths in the 10–100 nm range and by surface-sensitive X-ray photoemission spectroscopy at several specific capacities of the ZFO-C anodes. These techniques are shown to be able to provide information about the nature and extension of the individual chemical species within the SEI with a typical spatial resolution of 1–5 nm. A peculiar footprint of the interphase formations is obtained by comparing the chemical history of the reactive element sites in the anodes. The progressive development of the SEI in the first cycle and the variety of compositional transformations prior to stabilization are elucidated. Formation of a reversible alkyl carbonate layer, with maximum thickness of 7 nm, is detected at the SEI topmost region. On the basis of these results, we have obtained a map of suitable spatial resolution of the evolution of the different components of the interface layer.

The evolution of the solid electrolyte interphase (SEI) during the first Li uptake in advanced Li-ion electrodes is studied by X-ray absorption spectroscopy (XAS). The As atoms present in the electrolyte solution were used as a local probe for monitoring the SEI growth on different electrodes. High-quality As K-edge spectra were collected in fluorescence mode for a set of graphite and carbon-coated ZnFe2O4electrodes. XAS measurements have been preceded and corroborated by electrochemical characterizations. SEI phase evolution was analyzed by distinct As valence states in the subsequent stages of SEI formation, while X-ray fluorescence (XRF) was used to estimate the As content. Detailed structural results are presented for different Li contents in different electrodes including the estimated thickness of the SEI layer, contribution of different As oxidation states, and As local structure. The formation of AsFNcomplexes with different local coordination Nis clearly observed and measured at various SEI evolution stages. Evidence of a partially reversed redox process, taking place within the SEI by charge–discharge cycling, was also obtained.

Abstract

Abstract

Polypyrrole (pPy) thin films were synthesized electrochemically by a pulse method on platinum electrodes in N‐butyl‐N‐methyl‐pyrrolidinium bis(trifluoromethanesulfonyl)imide ionic liquid (PYR14TFSI). An important aspect of this procedure is the use of an ionic liquid, as synthetic medium. Further, it can be used for several procedures and it can then be renewed and recycled by a simple extraction just with warm water. It is therefore possible to remove it from all the residual oxidized pyrrolic compounds and purify the solvent in a very simplicistic way. After the synthesis pPy was overoxidized (opPy ) and the process was followed by EIS (Electrochemical Impedance Spectroscopy). opPy is attractive for the realization of sensors and biosensors because of its good selectivity towards hydrogen peroxide (H2O2) with respect to the most common interferents. In particular it can find an application in food process control. The EIS response to hydrogen peroxide and biological interferents indicated opPy as a highly sensitive electrochemical platform for impedimetric sensing. The glucose oxidase enzyme (GOD) was immobilized onto the polymer and the modified electrode was assembled and tested as an impedimetric biosensor. This technique seems very promising for application in food process control.

Phase diagrams are reported for mixtures between bis(trifluoromethanesulfonyl)imide (TFSI^-) salts containing Li⁺ and N-alkyl-N-methylpyrrolidinium (PYR1R⁺) cations. The latter salts readily form both room temperature ionic liquids and plastic crystalline phases. Mixed salt crystalline phases are found which are likely to influence the performance of such mixed salt systems when utilized as electrolytes for electrochemical devices as well as give insight into ionic liquid−solute interactions.

V2O5 aerogel (ARG) has been studied as an insertion host for lithium ions and for several polyvalent cations. The stability, reversibility, and capacity for ion insertion and release processes make the amorphous ARG an interesting material for battery applications. The local structural modifications resulting from the chemical insertion of Zn²⁺ ions into the host have been investigated by X-ray absorption spectroscopy (XAS). X-ray absorption near-edge structure (XANES) spectra at the V K-edge of ZnxV2O5 did not shown any substantive change as a function of increasing amounts of intercalated ions, thus indicating the absence of interactions between the intercalated ions and the vanadium ions. To study the structural sites of the polyvalent ions, EXAFS (extended X-ray absorption fine structure) spectra have been recorded at the Zn K-edge. The EXAFS analysis showed that the Zn²⁺ ions are 4-fold coordinated by almost coplanar oxygens. In addition, differences in the first shell of the inserted Zn²⁺ as a function of the intercalation level have been observed. The first-shell Zn−O bond length shortened and the EXAFS Debye−Waller factor increased. This suggests a decrease of the local geometrical order of the first shell as polyvalent cations are inserted.

Magnesium-substituted birnessite and zinc chalcophanite have been synthesized through a novel procedure based on a combination of coprecipitation and metal ion intercalation techniques. The materials showed very promising performance as hosts for lithium intercalation. Upon galvanostatic discharge, Mg−birnessite and Zn−chalcophanite composite cathodes were able to intercalate >2 equiv of lithium per mole.

Lithium insertion in metal oxides is a process of interest in many electrochemical applications, including rechargeable batteries and electrochromic displays. In this work we have examined the characteristics of this process in a series of oxides prepared in the thin-film configuration. The lithium insertion process has been examined in WO3, NiO, V2O5, Nb2O5 and tin-doped indium oxide (ITO) thin film electrodes deposited on transparent substrates. We have considered various aspects of the insertion process in these oxides with particular attention to charge capacity, reversibility, kinetics, structural and optical changes. The results suggest that the process may induce irreversible modifications in some of the host structures. However, under certain well defined conditions, the process occurs reversibly and thus some of the studied oxides may find successful application in electrochemical devices of prime technological interest.

The poly(ethylene oxide)-lithium tetrafluoborate complex, (PEO)7 LiBF4, has been characterized in terms of total and electronic conductivity, lithium transport number, stability versus lithium electrode and thermal properties. The results indicate that this polymeric electrolyte offers promises of application in lithium-based electrochemical devices.

The physico-chemical and electrochemical properties of a new class of polymer electrolytes formed by complexes of poly(ethylene oxide) and copper trifluorosulphonate salts have been investigated. The results suggest that these electrolytes are good copper ion conductors. Under particular conditions of concentration and temperature, and apparent electronic transport has also been evidenced.

Sodium-ion batteries (SIBs) are promising alternative to Lithium-ion batteries for massive stationary energy storage. To improve energy density, however, more performing active materials are needed. In order to allow sustainable scale-up, it is also mandatory to develop green products and processes. Herein, we report on anodes of phosphorus/carbon (P/C) nanocomposites prepared via High Energy Ball Milling (HEBM), a simple, powerful and easily scalable synthesis technique. The electrodes were prepared under oxygen-free atmosphere, using water as solvent, which enabled the use of aluminum (instead of copper) as current collector, implying significant cost reduction. The P/C nanocomposite obtained after 54 h HEBM resulted in excellent cycling stability, delivering very high specific capacity (2200 mAh g−1, C/20) and showing good capacity retention after 120 cycles. A careful structural analysis (XRD, FESEM-EDS, XPS), revealed that long milling times strongly increased cycling stability due to: (i) significant decrease of P particle size inside the matrix and deep composite amorphization, which alleviates the buffering dimensional issues typical of black phosphorus; (ii) presence of defects in the carbonaceous component, which allows easier Na+insertion into the anode. Our results show that P/C nanocomposites are very promising anode materials for SIBs, paving the way for further exploitation of nano-architectures in SIBs technology.

In this paper we report on the investigation of ionic liquid-based electrolytes with enhanced characteristics. In particular, we have studied ternary mixtures based on the lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) salt and two ionic liquids sharing the same cation (N-methyl-N-propyl pyrrolidinium, PYR13), but different anions, bis(trifluoromethanesulfonyl)imide (TFSI) and bis(fluorosulfonyl)imide (FSI). The LiTFSI-PYR13TFSI-PYR13FSI mixtures, found to be ionically dissociated, exhibit better ion transport properties (about 10−3S cm−1at −20°C) with respect to similar ionic liquid electrolytes till reported in literature. An electrochemical stability window of 5 V is observed in carbon working electrodes. Preliminary battery tests confirm the good performance of these ternary electrolytes with high-voltage NMC cathodes and graphite anodes.

In this study we compare the properties and the performance of three different carbonaceous materials, namely activated carbon, carbon black and graphene based nanoplatelets, as active materials for electrochemical double layer capacitors (EDLCs). The aim of this investigation is to contribute to the assessment of the advantages and limits related to the use of alternative active carbonaceous materials for EDLCs, with particular regard to carbon blacks. The results of this investigation indicate carbon black as a very promising candidate for the realization of high performance EDLCs, able to display high energy and high power. However, float test for 500 h at 2.7 V have shown strong capacitance fade for carbon black based EDLCs. Post-mortem SEM analysis revealed cracks in the electrode surface, which could be related to the breakage of carbon black agglomerates during float test, which then in turn may be the reason of the strong capacitance fade. Overcoming this issue will be the next challenging step in order to be able to take advantage of the promising characteristics of this carbon black for longer time periods.

Ion chromatography was used to investigate the stability of LiTFSI in water at various temperatures. The addition of HNO3, LiOH and HTFSI as pH adjustment measures was studied and the long-term stability of the electrolytes at different pH values stored at 60°C investigated. A minor degradation product was found upon the addition of HNO3to the electrolyte and identified via electrospray ionization mass spectrometry. The compound was formed only in traces immediately after the acidification and the concentration is not increasing over time. Electrochemical stability window investigations, using two different methods, indicate the wide applicable potential range of the aqueous LiTFSI electrolyte, which, combined with the high stability of the TFSI anion vs. hydrolysis and elevated temperature, smoothens the path for a possible application in aqueous lithium-ion systems.

In this paper we report on the use of a methacrylate-based gel polymer electrolyte (GPE) in high power devices. Methacrylate-based GPEs display high mechanical stability and good conductivity, thus they can be successfully employed for the use in supercapacitors (SCs). As a matter of fact, SCs with an operative voltage of 3.0 V were realized using the investigated GPE, which were able to display high energy, power and promising cycling stability. These electrolytes were also tested for application in lithium-ion capacitors (LICs). It is shown herein for the first time that it is possible to cycle a LIC with an operative voltage of 4.0 V using the methacrylate-based GPE, with a high energy and a stable performance over 100,000 cycles.

Coating of electrode materials for lithium-ion batteries is usually performed in order to improve performance, safety and the processability of the raw material. Here, we apply a dry coating method of graphite with hydrophobic fumed silica particles. This method excludes the use of any harmful solvents and the nano-scale particles cover and stick to the graphite substrate by only adhesive forces. Furthermore, this dry coating method is easily mass-scalable and a high throughput can be obtained in a short processing time. The nanoparticle coating reduces the van-der-Waals forces between the graphite particles and leads in this way to better flowability of the graphite powder which is important for further processing and the production of electrode tapes. Furthermore, these core-shell particles were processed to composite negative graphite electrodes in combination with the water soluble binder sodium carboxy-methylcellulose. Electrodes obtained with the coated material displayed a smooth surface, a high mechanical stability and outperformed the unmodified ones in the electrochemical investigations.

The combined use of soft carbon (PeC) as anodic material, and propylene carbonate (PC) as electrolyte solvent is a promising strategy for the realization of high performance lithium-ion capacitors (LIC). PeC electrodes display a capacity of around 80 mAhg−1during cycling carried out at 5C, which can be maintained for more than 10,000 cycles. This performance is higher than that displayed by most of the carbonaceous electrodes so far proposed for LIC. PC is known to be a safer electrolyte compared to mixtures of organic carbonates used so far in LIC, and therefore its use is beneficial for the realization of safer LIC. When a correct pre-lithiation process is applied, LICs based on PeC and PC display high performance in terms of capacity and cycling stability. When a current density of 10.6 mA/cm2(corresponding to 5.6 A/g) is applied to a LIC average energy and power of 21.7 Wh kg−1and 4.1 kW kg−1(based to the total active material), respectively, were achieved.

The stringent environmental requirements regarding the mobility energy usage are forcing most automakers to develop hybrid electric vehicles, which allows for a more efficient and thus less polluting use of fossil combustibles. A vast deployment of such vehicles involves producing and recycling of batteries on the thousand tons per year scale. Present Li-ion technologies involve the use of fluorinated binders, which are costly, and the use of environmentally unfriendly volatile organic compounds for the processing, which are difficult to recycle. In this paper, it is shown that the fluorinated binders can be replaced with greener and cost-effective polymers derived from cellulose.

In this work is described an improved synthesis of hydrophobic room-temperature ionic liquids (RTIL) composed of N-methyl-N-alkylpyrrolidinium (or piperidinium) cations and (perfluoroalkylsulfonyl)imide, [(CnF2n+1SO2)(CmF2m+1SO2)N−], anions. The procedure described allows the synthesis of hydrophobic ionic liquids with the purity required for electrochemical applications such as high-voltage supercapacitors and lithium batteries. This new synthesis does not require the use of environmentally unfriendly solvents such as acetone, acetonitrile, and alogen-containing solvents that are not suitable for industrial applications. Only water and ethyl acetate are used throughout the entire process. The effect of the reaction temperature, time, and stoichiometry in the various steps of the synthesis has been investigated. With an iterative purification step performed at the end of the synthesis, ultrapure, clear, colorless, inodorous RTILs were obtained. The final vacuum drying at 120°Cgave RTILs with a moisture content below 10ppm. Details for the synthesis of N-butyl-N-methylpyrrolidinium bis(trifluoromethansulfonyl)imide (PYR14TFSI)are reported. The overall yield for the synthesis of this ionic liquid was above 86wt%. Electrochemical tests performed on this material are also reported.

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