Two lithium-ion hybrid supercapacitors (LiHSs) based on high power active materials like Li3V1.95Ni0.05(PO4)(3)/C (LVNP/C), Li4Ti5O12 (LTO) and activated carbon (AC) are investigated as high energy and high power devices. Both LiHSs are assembled by using a bi-material negative LTO:AC electrode (50 : 50), able to deliver 38.3 mAh g(-1) at 35 A g(-1) (200 C for LTO), and to retain 80 % of the initial capacity over 10000 cycles at 17.5 A g(-1). Two positive electrodes are employed in complete devices: a battery-type LVNP/C and a bi-material LVNP/C:AC (65 : 35) based electrodes, for two LiHSs named Hybrid A and Hybrid B, respectively. The energies of the LiHSs are evaluated from 0.05 to 10 A g(-1), and at different cell voltages (2.6, 2.7 and 2.8 V). The best performance is obtained with Hybrid A cycled between 0-2.7 V, that with 36.3 Wh L-1 at 4.3 kW L-1, possesses an energy density five time higher than that of the AC||AC (6.8 Wh L-1). Despite both LiHSs charged up to 2.8 V possess superior energy values, at this cell voltage Hybrid A and Hybrid B retain only 11 % and 8 % of the initial capacity cycled over 8000 cycles at 10 A g(-1), respect to the 75 % and 81 % of the same systems cycled up to 2.7 V.

Abstract The operation principles of batteries and, more generally, of all classes of electrochemical power sources, are introduced. Then, the roles of electrodes and electrolyte during charge and discharge processes are presented. The energy content of batteries is explained in terms of theoretical cell voltage and capacity. The basic thermodynamics laying the foundations of the redox processes which take places at the electrodes is presented, and the Nernst's equation is introduced, with the aim to describe the electrode potentials generating the cell voltage. At the same time, the capacity of the active materials is derived on the basis of Faraday's law. The kinetics of the interfacial redox processes is described with particular attention to the mechanisms of charge‐transfer and to electron and ion conduction, explaining the origin of cell polarization and overvoltage. The impact of thermodynamics and kinetics onto performances is then rationalized by introducing practical operating parameters such as coulombic efficiency, capacity retention, cycle life, and rate capability. Finally, an overview of some of the main classes of primary and secondary batteries, as well as a comparison with alternative electrochemical storage systems such as fuel cells, is given.

Non-fluorinated Li3V1.95Ni0.05(PO4)(3)/C-based electrodes were prepared by using sodium carboxymethyl cellulose, sodium alginate and poly(acrylic acid) as alternative binders of the standard poly(vinylidene difluoride). The effect of the binders was investigated on several aspects, starting from the rheological properties of the dispersions, to the physical-chemical properties of the layers (adhesion test, electrode porosity, surface conductivity). The prepared Li3V1.95Ni0.05(PO4)(3)/C-based electrodes were characterized as cathodes at different C-rates ranging from 1 C to 200 C in two different potential windows, between 3.0-4.3 and 3.0-4.8 V vs. Li/Li+. The cycle life of the LVNP/C-based electrodes was characterized for each potential window at C-rate as high as 100 C and for 10000 cycles. Electrochemical impedance spectroscopy, scanning electrode microscopy, X-ray diffraction and energy dispersive X-ray measurements were used to study the aged electrodes. Among the electrodes, the one prepared with Na-alginate binder displays the best electrochemical performance, with a specific capacity of 100 and 85 mAh g(-1) delivered at 100 C when charged up to 4.3 and 4.8 V vs. Li/Li-vertical bar, respectively. Moreover, in the same potential windows, it displays an excellent cycling stability over 10000 cycles at 100 C, with a capacity retention of 80% and 65%. (C) 2017 The Electrochemical Society. All rights reserved.

Herein, we report for the first time the use of a protic ionic liquid as a component of a new Na-ion battery electrolyte. The protic ionic liquid has been tested in combination with two different types of sodium-ion cathode materials, polyanionic Na3V2(PO4)(3) and layered Na0.67Mn0.89Mg0.11O2, in order to reveal its impact on the electrode material electrochemical performance. The results evidence that this novel electrolyte performs very well in combination with a polyanionic electrode material, while it shows poor performance with a layered oxide material.

Exceptionally high specific capacities at ultrahigh charge/discharge currents have been obtained with a bi-material electrode prepared using Li3V1.95Ni0.05(PO4)(3)/C (LVNP/C) and activated carbon (AC) as coexisting active materials. Thanks to the amphoteric properties of LVNP/C, this electrode designated as LVNP/C-AC, has been evaluated both as positive and negative electrode in 1 M LiPF6 in EC:DMC (1:1). At high specific currents (26.6 Ag-1), the bi-material electrode delivers specific capacities as high as 61 and 24 mAh g(-1), between 3.0-4.3 V and 3.0-1.5 V vs Li/Li+, respectively. By contrast, the corresponding values for LVNP/C are 49 and 18 mAh g(-1). In both potential windows, the bi-material electrode shows an excellent cycling stability over 2000 cycles at 26.6 A g(-1), with capacity retention of 95 and 89%, between 3.0-4.3 and 3.0-1.5 V vs Li/Li+, respectively. The synergic effect of the activated carbon on the electrochemical performances of Li3V1.95Ni0.05(PO4)(3)/C is investigated by comparing the cyclic voltammetry, electrochemical impedance spectroscopy, electronic conductivity, galvanostatic cycling, and scanning electron microscopy of the bi-material electrode with the ones of LVNP/C. This study highlights the huge potentialities of this bi-material electrode for the development of high energy and high power Li-ion hybrid supercapacitors. (C) 2016 Elsevier Ltd. All rights reserved.

A polyoxometalates (POM) of Kegging-type structure, Cs3HPMo11VO40 has been tested as mesoporous matrix to increase Pt electrocatalytic activity, by the enhancement of particles dispersion and active area. Physicochemical characterization has been carried out to clarify the structural properties of the matrix. SEM micrograph demonstrated a big change of the morphological features identifying POMs crystals with diameter less than 500 nm. The composite catalyst has been prepared by mixing the polyoxometalates with Pt/Vulcan XC72-R catalyst. By RRDE studies, an improvement in catalytic activity has been observed, both for HOR and ORR, for the layer modified with polyoxometalate matrix. Carbon monoxide adsorption/desorption processes have been also studied in order to evaluate any possible effect towards CO poisoning. Finally, the behavior of a fuel cell, prepared with a POM-modified cathode, was evaluated at 100% relative humidity, revealing that a lower Pt loading can be applied in presence of POM co-catalyst, yielding uncompromised and durable performance. (C) 2016 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.

The catalytic activity of commercial Pt nanoparticles mixed with mesoporous polyoxometalate Cs3H2PMo10V2O40 towards oxygen reduction reaction is evaluated. The polyoxometalate co-catalyst is prepared by titration of an aqueous solution of phosphovanadomolibdic acid. SEM micrography shows reduction particle size to less than 300 nm, while XRD confirms that the resulting salt maintains the Kegging structure. The composite catalyst is prepared by mixing the POM salt with Pt/C by sonication. RRDE studies show better kinetics for ORR with low Pt loading at the electrode surface. A MEA is assembled by using a Pt/POM-based cathode, in order to assess performance in a working fuel cell. Current vs. potential curves reveals comparable or better performances at 100%, 62% and 17% relative humidity for the POM-modified MEA with respect to a commercial MEA with higher Pt loading at the cathode. Electrochemical impedance spectroscopy (EIS) confirms better kinetics at low relative humidity. Finally, an accelerated stress test (AST) with square wave (SW) between 0.4 V and 0.8 V is performed to evaluate MEA stability for at least 100 h and make predictions about lifetime, showing that after initial losses the catalytic system can retain stable performance and good morphological stability. (C) 2016 Elsevier B.V. All rights reserved.

Synthetic LiFe1-xZnxPO4 (0 <= x <= 0.26) samples have been prepared using wet chemistry method. The samples have been characterized by means of Rietveld structure refinement of Powder-XRD data and by Mossbauer spectroscopy. Impurities such as Li3PO4 and Fe2P have been detected in small amount and quantified by Rietveld analysis. No Zn-bearing impurity has been detected up to x = 0.15, but significant amounts of LiZnPO4 have been observed in the samples with x >= 0.2. The unit cell volume of LiFePO4 decreases anisotropically with increasing Zn content (-0.7% of initial volume of 291.343 angstrom(3)). Cell parameter (orthorhombic Pbnm space group, #62) b(0) and c(0) decrease with increasing Zn content, whereas a(0) parameter is almost constant. The average and interatomic distances in the M1 and M2 sites are almost constant, whereas the distance slightly decreases (-1.4% of the initial value). Interestingly, O2-O1-O2 bond angle along the [001] direction decreases with increasing Zn-content, thus resulting in a marked decrease of the c(0) axis length although the distance remains essentially constant. Mossbauer analyses show the majority of Fe to be divalent and located in an octahedral site similar to available literature data for LiFePO4. The Fe3+/(Fe3++Fe2+) ratio ranges from 0.10 to 0.17, and is not related to the Zn content. Preliminary electrochemical analyses of Zn doped samples in comparison to pristine LiFePO4 are reported. (C) 2015 Elsevier B.V. All rights reserved.

Boosted by costs benefits, the development of room temperature Na-ion batteries is strongly desired for stationary applications. In this study we explore the possible use of V2O5 aerogel as anode material for sodium ion batteries. The aerogel is able to reversibly insert more than 3 Eq. of sodium in the voltage range 0.1 V-4 V vs. Na/Na+ demonstrating to possess additional capacity when cycled to lower voltage. The anode delivers about 200 mAh g(-1) in the voltage range 0.01 V-1.5 V vs. Na/Na+. The preliminary characterization of a full Na-ion cell made coupling the V2O5 aerogel anode with carbon-coated Na3V2(PO4)(3) cathode is also reported. The cell, showing an average voltage of 2.5 V, performed 200 cycles with good efficiency and a maximum specific capacity of 113 mAh per gram of anode material. (C) The Author(s) 2015. Published by ECS. All rights reserved.

An advanced lithium ion battery using nanostructured tin-carbon lithium alloying anode and high voltage LiNi0.5Mn0.5O4 spinel-type cathode is studied, with particular focus to the low temperature range. The stable behavior of the battery is assured by the use of an electrolyte media based on a LiPF6 salt dissolved in EC-DEC-DMC, i.e. a mixture particularly suitable for the low temperature application. Cycling tests, both in half cells and in full lithium ion battery using the Sn-C anode and the LiNi0.5Mn0.5O4 cathode, performed in a temperature range extending from room temperature to 30 degrees C, indicate that the electrode/electrolyte configuration here adopted may be suitable for effective application in the lithium ion battery field. The full cell, cycled at -5 degrees C, shows stable capacity of about 105 mAh g(-1) over more than 200 charge-discharge cycles that is a relevant performance considering the low temperature used for the study. (C) 2014 Elsevier B.V. All rights reserved.

A structural study of Pt nano-catalysts is presented in the paper. The innovation in the case of the considered catalytic materials resides in the use a meso-microporous inorganic matrix of heteropolyacid salt of composition X2.5H0.5YMo12O40 where X=Rb, Cs and Y=P, Si as a catalyst support. Metallic nanoparticles were created by platinum ions reduction in a hot H2/Argon stream and were mainly located into matrix pores. As the porous structure can be controlled by the type and content of the cation used, the desired/optimal Pt nanoparticle size can be precisely defined by using a proper heteropolyacid salt composition. Multiple-scattering extended X-ray absorption fine structure (MS EXAFS) analysis was applied to obtain the relation between the matrix composition and the size of the catalyst nanoparticles. The results showed that it was only the secondary structure form of the heteropolymolybdate salt (i.e. Rb or Cs cations) that influenced the metallic nanoparticle size. The smaller the X atom ionic radii, the larger the mean diameter of the embedded Pt nanoparticles.

Nanostructured Li3V2−xNix(PO4)3(x= 0, 0.05, and 0.1) cathodes, thanks to their high rate capability and excellent cycle stability, are proposed as excellent candidates for the development of high energy and high power density Li-ion asymmetric supercapacitors.

A graphene-based composite containing Sn and Sb is synthesized and characterized. Structural and morphological characterizations demonstrate the achievement of multilayer graphene with anchored SnSb nanoparticles. The composite is tested as active material for lithium-ion battery anodes and, as a result of the use of poly acrylic acid binder and vinylene carbonate electrolyte additive, remarkable electrochemical performance are achieved in terms of stable cycling stability and specific gravimetric capacity (468 mAh g−1 after 75 cycles with a capacity retention of about 80%). Moreover, impedance spectroscopy analysis further demonstrates the enhanced stability obtained by using, together with vinylene carbonate electrolyte additive, poly acrylic acid binder instead of poly vinylidene difluoride.

The electrochemical behavior of a composite anode based on tin oxide nanoparticles embedded in electrically conductive graphene matrix is reported. The composite has been synthetized through microwave reduction of poly acrylic acid functionalized graphene oxide and a tin oxide organic precursor both dispersed in ethylene glycol. The poly acrylic functionalization of graphene oxide partially prevent the re-stacking of the graphene layers. In addition, poly acrylic acid acts as a surfactant favoring an optimized dispersion of the metal and, after thermal decomposition, contributes in creating a carbon layer for an improved conductivity. The final product morphology reveals a composite in which SnO2 nanoparticles are homogenously distributed into the reduced graphene oxide matrix. Graphene/SnO(2)nanocomposite electrodes, prepared using Super-P carbon as conducting additive and polyvinylidenedifluoride as binder, exhibit high rate capability and cycle life during galvanostatic charge/discharge tests. After more than 140 cycles, mostly performed at 500 mAg(-1), the electrodes show a remarkable stable specific capacity of about 430 mAh g(-1) with a Coulombic efficiency close to 100%.The morphological stability of the electrode is also confirmed by impedance spectroscopy analysis, which shows solid-electrolyte interphase related resistance values constant up to 100 cycles. (C) 2014 Elsevier Ltd. All rights reserved.

In this paper we present detailed X-ray absorption fine structure (XAFS), X-ray diffraction (XRD) and transmission electron microscopy (TEM) investigations of the changes in the local geometric and electronic structure of Pt nanoparticles used as a cathode catalyst in proton exchange membrane fuel cell (PEMFC), working under controlled potential cycling conditions. The body of the results obtained suggests that in the first stage of PEMFC operation, small particle dissolution was a dominant process. Subsequent 100h of work led to the progressive agglomeration of nanoparticles followed by a pronounced growth of the mean nanoparticle size. At the same time, high-quality XAFS spectra analysis demonstrated that negligible changes in structural local ordering and a slight increase in Pt 5d-electron density occurred during the whole FC operation period under consideration.

A graphene/silicon nanocomposite has been synthesized, characterized and tested as anode active material for lithium-ion batteries. A morphologically stable composite has been obtained by dispersing silicon nanoparticles in graphene oxide, previously functionalized with low-molecular weight polyacrylic acid, in eco-friendly, low-cost solvent such as ethylene glycol. The use of functionalized graphene oxide as substrate for the dispersion avoids the aggregation of silicon particles during the synthesis and decreases the detrimental effect of graphene layers re-stacking. Microwave irradiation of the suspension, inducing reduction of graphene oxide, and the following thermal annealing of the solid powder obtained by filtration, yield a graphene/silicon composite material with optimized morphology and properties.Composite anodes, prepared with high-molecular weight polyacrylic acid as green binder, exhibited high and stable reversible capacity values, of the order of 1000 mAh g(-1), when cycled using vinylene carbonate as electrolyte additive. After 100 cycles at a current of 500 mA g(-1), the anode showed a discharge capacity retention of about 80%. The mechanism of reversible lithium uptake is described in terms of Li-Si alloying/dealloying reaction. Comparison of the impedance responses of cells tested in electrolytes with or without vinylene carbonate confirms the beneficial effects of the additive in stabilizing the composite anode. (C) 2014 Elsevier B.V. All rights reserved.

A unique preparation method of obtaining stable composite film (with ultra-low platinum content) highly active towards oxygen reduction and hydrogen oxidation is presented here. The matrix for platinum centers consists of high-surface-area zeolite-type acidic salt of cesium phosphododecatungstate (Cs 2.5 H 0.5 PW 12 O 40 ) admixed with carbon (Vulcan XC-72) carriers. Platinum nanoparticles were deposited on the working electrode modified with matrix via corrosion of platinum counter electrode during cyclic voltammetry experiment conducted in acid electrolyte containing chloride ions. The results obtained from rotating disk voltammetry revealed that the composite film containing Pt nanoparticles at very low loadings (on the level of 2–5 μg cm −2 ) demonstrated remarkable electrocatalytic activity towards both oxygen reduction and hydrogen oxidation, particularly, when compared to the performance of the Cs 2.5 H 0.5 PW 12 O 40 -free system (i.e., containing only Vulcan support) prepared and examined under analogous conditions. The phenomenon should be primarily ascribed to the mesoporous nature of the matrix enabling immobilization and stabilization of small catalytic nanoparticles (1–2 nm diameters) inside the pores as well as to high surface acidity of the polyoxometalate-based salt providing proton-rich environment at the electrocatalytic interface.

Submicron-structured Li3V2(PO4)(3)/C has been synthesized by carbon-thermal reduction method with poly(acrylic acid) and D-(+)-glucose as carbon sources. The pure monoclinic structure of Li3V2(PO4)(3)/C has been confirmed by XRPD and Rietveld refinement, scanning electron microscopy, and transmission electron microscopy. The specific capacity of Li3V2(PO4)(3)/C as cathode has been evaluated, between 3.0 and 4.3 V vs Li+/Li, in the two different electrolytes: 1 M solution of LiPF6 in EC:DMC (1:1) at room temperature and in EC:DMC:DEC (1:1:1) at low temperature (0 and -20 degrees C). Because of the submicron-size dimensions of Li3V2(PO4)(3) and of the good carbon coating, the material discharge capacities as high as 103, 98 and 81 mAh g(-1) at 40, 60 and 100C rates, retains 93% of the initial discharge capacity after 1000 cycles at 100C. The performances even at low temperature are also good with values of the order of 84, 40, 23, 19 mAh g(-1) at 0 degrees C and 69, 24, 19, 15 mAh g(-1) at -20 degrees C at 3, 7.5, 15, 30 C-rates, respectively. (C) 2014 Elsevier B.V. All rights reserved.

Composite anodes based on Si and reduced graphene oxide (RGO) have been prepared using commercial Si nanopowder, graphene oxide (GO) and polyacrilic acid (PAA) as starting materials. A double reduction step, consisting in microwave irradiation at mild power followed by thermal annealing in reducing atmosphere, yielded the composite powder made of Si:reduced graphene oxide (RGO) in the approximate mass ratio 30:70. The charge/discharge properties of the anode materials are determined by the homogeneous dispersion of Si grains between RGO nanosheets, that act as structural buffer for volume changes related to Li-Si reversible alloying and as improved electrical conductor. Electrodes have been prepared using high-molecular weight PAA as binder, which promises better mechanical stability towards silicon volume changes. The electrochemical behavior of the composite anode material has been characterized by galvanostatic cyclations and electrochemical impedance spectroscopy, using LiPF61M in EC:DMC 1:1 electrolyte, also modified by the addition of 5% vinylene carbonate (VC). Several anodes have been investigated, consistently delivering reversible capacities higher than 1000 mAhg-1, with a mechanism that, after initial lithiation of crystalline Si, mainly involves reversible Li-Si alloying/dealloying between amorphous a-Li and a-LixSi phases. Particularly, when cycled in VC-modified electrolyte the anode exhibits a remarkable cycle life, resulting in a residual capacity of more than 900 mAhg-1 after 60 cycles at 500 mAg-1 and efficiency values close to unity. Several factors concur in determining this behavior, namely: (i) the efficient Si dispersion in RGO carbonaceous matrix; (ii) the good mechanical properties of PAA binder; (iii) the formation of a stabilized SEI by VC additive in the electrolyte.