A regenerative fuel cell (RFC) is a hydrogen accumulator which is charged via an electrolyzer (electricity conversion into H2) and discharged via the fuel cell (H2 conversion into electricity), where the storage media is pressurized hydrogen. The also generated oxygen is mostly not stored in terrestrial applications. There are discrete RFCs (DRFC) consisting of two separate stacks (electrolyzer and fuel cell) and unitized RFCs (URFC) with one single stack working during charge in electrolysis mode and during discharge in fuel cell mode. URFCs show a high specific energy up to 1500 Wh kg−1. Furthermore, it is possible to optimize the power and energy of the system independently, which is important for seasonal storage of larger amounts of energy. In contrast to conventional electrochemical accumulators the discharge power of RFCs is unaffected by the state-of-charge of the system. But unfortunately, due to the long conversion chain with associated losses, RFCs generally have low levels of efficiency compared to conventional electrochemical accumulators. The high specific energy of URFCs makes the system interesting for niche applications in military and space areas where efficiency and related costs are not primary parameters. For civil terrestrial applications, however, costs and electrical efficiency are mostly primary parameters. DRFCs are preferred since the individual stacks (EL, FC) can be better optimized. However, for the time being, there are existing no commercial applications of RFCs, as they are not really competitive, especially not with electrochemical accumulators. In the future could be electricity storage with RFCs possible in off-grid or island applications in which a high level of autonomy is required but also in grid application with high share of renewables to stabilized power supply. In a broader sense are power-to-gas storage systems identically with DRFCs. Power-to-gas technologies and therefore also electrolyzers currently are developing strongly which will decreases the costs and increases the efficiency of RFC as well. The RFC technology is in the moment proton exchange membranes based, but they are relatively costly caused by use of platin group metal catalysts. Alkaline-RFCs could reduce the cost by using non-platin group metal catalysts. Because Alkaline–RFCs show an unsatisfactory performance and poor cyclability, therefore, the development is still in an initial stage. The efficiency of PEM-RFCs (URFC max. 35%, DRFC max. 40%) is relatively low. Higher efficiencies, however, show SO-RFCs. SO-URFCs already reach today in an early development state ca. 45% efficiency and could be used also in terrestrial applications.

The synthesis, characteristics and properties of a PEO-based, dry composite electrolyte are presented and discussed. The major feature of this electrolyte is the high stability towards the lithium metal electrode. This unique property makes the electrolyte quite promising for the development of rechargeable polymer lithium batteries.

Rechargeable, polymer lithium batteries are today considered as very promising advanced power sources for electric vehicle and/or consumer electronics. Many polymer electrolytes, some of which having very high ambient temperature conductivity, have been developed and characterized. However, very little attention has been so far dedicated to the study of the characteristics of the lithium electrode interface. Since the clarification of the interfacial phenomena is crucial in assessing the effective impact of polymer batteries, we have undertaken a detailed investigation of the Li passivation processes in most relevant electrolyte media and in this work we report results obtained in highly conductive cells using electrolytes formed by the immobilization of lithium solvates in polymer networks.

We have designed a self-standing anode built-up from highly conductive 3D-sponged nanofibers, that is, with no current collectors, binders, or additional conductive agents. The small diameter of the fibers combined with an internal spongelike porosity results in short distances for lithium-ion diffusion and 3D pathways that facilitate the electronic conduction. Moreover, functional groups at the fiber surfaces lead to the formation of a stable solid-electrolyte interphase. We demonstrate that this anode enables the operation of Li-cells at specific currents as high as 20 A g-1 (approx. 50C) with excellent cycling stability and an energy density which is >50% higher than what is obtained with a commercial graphite anode.

The potential for metallic lithium batteries that exhibit high specific capacities has stimulated a large interest within the energy research field. For safety reasons, the use of metallic lithium anodes requires electrochemically stable electrolytes. However, to date there has been limited success in this area. This work introduces a solid, lithium single-ion conductor thus providing new perspectives in the field of solid-state lithium-batteries. This new-concept material (LiFT), obtained by a direct reaction of nanometric fluorinated titanium oxide (FT) with molten metallic lithium, consists of nanoparticles (NPs) with anionic surface groups that are neutralized with lithium cations. The material displays fast lithium ion transport via an efficient migration mechanism occurring at the interfaces between different nanoparticles. The electrolyte comprises 1.34 mol kg(-1) of Li and a conductivity of 2.8.10(-4) S cm(-1) at 25 degrees C is demonstrated. This level of performance, in conjunction with a native electrochemical stability towards lithium, extremely low cost starting materials (TiO2) and a facile one-pot synthesis, renders this electrolyte very attractive for applications in future full solid-state lithium batteries.

A comparative study of sulfur composites using carbon of various natures, namely, graphite, mesocarbon microbeads, and multi-walled carbon nanotubes, is performed in lithium battery design and evaluation. Morphological and structural analyses, by means of SEM and XRD, cyclic voltammetry and galvanostatic cycling in lithium cells are employed for characterization of the materials. Tetraethylene glycol dimethyl ether containing lithium trifluoromethansulfonate is considered the preferred electrolyte for performing the electrochemical tests. Prior to use in cells, the electrolyte characteristics in terms of H-1, Li-7, and F-19 nuclei self-diffusion coefficients, ionic conductivity, and ionic association degree are studied by combining NMR and impedance spectroscopy. The best lithium-sulfur composite reported herein achieves a capacity higher than 500mAhg(-1) over 140cycles with no sign of dendrite formation or failure. This performance is considered sufficiently suitable for the development of high-energy lithium batteries, in particular, considering the expected safety of the cells by employing a nonflammable glyme electrolyte instead of a conventional carbonate-based one.

Here, two ionic liquids, N-ethoxyethyl-N-methylmorpholinium bis(trifluoromethanesulfonyl)imide (M1,2O2 TFSI) and N-ethoxyethyl-N-methylpiperidinium bis(trifluoromethanesulfonyl)imide (P1,2O2 TFSI) were synthesized and compared. Fundamental relevant properties, such as thermal and electrochemical stability, density, and ionic conductivity were analyzed to evaluate the effects caused by the presence of the ether bond in the side chain and/or in the organic cation ring. Upon lithium salt addition, two electrolytes suitable for lithium batteries applications were found. Higher conducting properties of the piperidinium-based electrolyte resulted in enhanced cycling performances when tested with LiFePO4 (LFP) cathode in lithium cells. When mixing the P1,2O2 TFSI/LiTFSI electrolyte with a tailored alkyl carbonate mixture, the cycling performance of both Li and Li-ion cells greatly improved, with prolonged cyclability delivering very stable capacity values, as high as the theoretical one in the case of Li/LFP cell configurations.

The room-temperature molten salt mixture of N,N-diethyl-N-(2-methoxyethyl)-N-methylammonium bis(trifluoromethanesulfonyl) imide ([DEME][TFSI]) and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) salt is herein reported as electrolyte for application in Li-O2 batteries. The [DEME][TFSI]-LiTFSI solution is studied in terms of ionic conductivity, viscosity, electrochemical stability, and compatibility with lithium metal at 30 °C, 40 °C, and 60 °C. The electrolyte shows suitable properties for application in Li-O2 battery, allowing a reversible, low-polarization discharge-charge performance with a capacity of about 13 Ah g-1carbon in the positive electrode and coulombic efficiency approaching 100 %. The reversibility of the oxygen reduction reaction (ORR)/oxygen evolution reaction (OER) is demonstrated by ex situ XRD and SEM studies. Furthermore, the study of the cycling behavior of the Li-O2 cell using the [DEME][TFSI]-LiTFSI electrolyte at increasing temperatures (from 30 to 60 °C) evidences enhanced energy efficiency together with morphology changes of the deposited species at the working electrode. In addition, the use of carbon-coated Zn0.9 Fe0.1 O (TMO-C) lithium-conversion anode in an ionic-liquid-based Li-ion/oxygen configuration is preliminarily demonstrated.

Suitably selected ionic liquids (ILs) are first applied as antistatic agents for poly(methyl methacrylate) (PMMA) and poly(butyl methacrylate) (PBMA) films in this study. We have compared volume- and surface-resistivity (Rv and Rs) on the basis of the morphology of the composite films. These values were found to deeply relate to the compatibility. For pure polymer films, both Rv and Rs were found to be around 1012Ωcm and 1014Ωcm−2, respectively at 60°C. These values were reduced hundred times by adding 10wt% of the ILs having a high compatibility with polymer matrices. When the compatibility is good enough, ILs are uniformly incorporated into the matrices, and accordingly the films are properly plasticized and fully transparent. We also show that the incorporation of ILs, having poor compatibility with polymethacrylates, results in the turbid films with a concomitant reduction of Rs but not of Rv, attributed to the bleed out of the ILs from the films. We believe that assuring the transparency of the film and suppressing undesired washing out effect of ILs are major tasks, and hence, we conclude that ILs showing high affinity with polymethacrylates are the most promising antistatic agents for polymethacrylates.

We unravel the role of flake dimensionality on the lithiation/de-lithiation processes and electrochemical performance of anodes based on few-(FLG) and multi-layer graphene (MLG) flakes prepared by liquid phase exfoliation (LPE) of pristine graphite. The flakes are sorted by lateral size (from 380 to 75nm) and thickness from 20 (MLG) to 2nm (FLG) exploiting a sedimentation-based separation in centrifugal field and, finally, deposited onto Cu disks for the realization of four binder-free anodes. The electrochemical results show that decreasing lateral size and thickness leads to an increase of the initial specific capacity from ≈590 to ≈1270mAhg−1. However, an increasing irreversible capacity is also associated to the reduction of flakes’ size. We find, in addition, that the preferential Li ions storage by adsorption rather than intercalation in small lateral size (<100nm) FLG flakes has a detrimental effect on the average de-lithiation voltage, resulting on low voltage efficiency of these anodes. We believe that the results reported in this work, provide the guidelines for the practical exploitation of graphene-based electrodes.

Electrochemical energy storage devices based on Li-ion cells currently power almost all electronic devices and power tools. The development of new Li-ion cell configurations by incorporating innovative functional components (electrode materials and electrolyte formulations) will allow to bring this technology beyond mobile electronics and to boost performance largely beyond the state-of-the-art. Here we demonstrate a new full Li-ion cell constituted by a high-potential cathode material, i.e. LiNi0.5Mn1.5O4, a safe nanostructured anode material, i.e. TiO2, and a composite electrolyte made by a mixture of an ionic liquid suitable for high potential applications, i.e. Pyr1,4PF6, a lithium salt, i.e. LiPF6, and standard organic carbonates. The final cell configuration is able to reversibly cycle lithium for thousands of cycles at 1000 mAg−1 and a capacity retention of 65% at cycle 2000.

Increased pollution and the resulting increase in global warming are drawing attention to boosting the use of renewable energy sources such as solar or wind. However, the production of energy from most renewable sources is intermittent and thus relies on the availability of electrical energy-storage systems with high capacity and at competitive cost. Lithium-sulfur batteries are among the most promising technologies in this respect due to a very high theoretical energy density (1675 mAh g-1 ) and that the active material, sulfur, is abundant and inexpensive. However, a so far limited practical energy density, life time, and the scaleup of materials and production processes prevent their introduction into commercial applications. In this work, we report on a simple strategy to address these issues by using a new gel polymer electrolyte (GPE) that enables stable performance close to the theoretical capacity of a low cost sulfur-carbon composite with high loading of active material, that is, 70 % sulfur. We show that the GPE prevents sulfur dissolution and reduces migration of polysulfide species to the anode. This functional mechanism of the GPE membranes is revealed by investigating both its morphology and the Li-anode/GPE interface at various states of discharge/charge using Raman spectroscopy.

This article provides the first comprehensive review of the most recent class of lithium-ion battery materials, hosting lithium by a combined conversion/alloying mechanism.

A novel, low cost and environmentally sustainable lithium sulfide-carbon composite cathode, suitably prepared by combining polyethylene oxide (PEO), LiCF3SO3 and Li2S-C powders is here presented. The cathode is characterized in lithium-metal cell employing a solution of LiCF3SO3 salt in dioxolane-dimethylether (DOL-DME) as the electrolyte. Detailed NMR investigation of the diffusion properties of the electrolyte is reported in order to determine its suitability for the proposed cell. The addition of LiNO3 to the electrolyte solution allows practical application in a lithium sulfur cell using the Li2S-C-based cathode characterized by a specific capacity of about 500 mAh g-1 (as referenced to the Li2S mass). The cell holds its optimal performances for over 70 cycles at C/5 rate, with a steady state efficiency approaching 99%. X-ray diffraction patterns of the cell upon operation suggest the reversibility of the Li2S electrochemical process, while repeated electrochemical impedance spectroscopy (EIS) measurements indicate the suitability of the electrode-electrolyte interface in terms of low and stable cell impedance. Furthermore, the EIS study clarifies the activation process occurring at the Li2S cathode during the first charge process, leading to the decrease of the cell polarization during the following cycles. The data here reported shed light on important aspects to be considered for the efficient application of the Li2S cathode in lithium battery.

In this paper, we report an advanced long-life lithium ion battery, employing a Pyr14 TFSI-LiTFSI non-flammable ionic liquid (IL) electrolyte, a nanostructured tin carbon (Sn-C) nanocomposite anode, and a layered LiNi1/3 Co1/3 Mn1/3 O2 (NMC) cathode. The IL-based electrolyte is characterized in terms of conductivity and viscosity at various temperatures, revealing a Vogel-Tammann-Fulcher (VTF) trend. Lithium half-cells employing the Sn-C anode and NMC cathode in the Pyr14 TFSI-LiTFSI electrolyte are investigated by galvanostatic cycling at various temperatures, demonstrating the full compatibility of the electrolyte with the selected electrode materials. The NMC and Sn-C electrodes are combined into a cathode-limited full cell, which is subjected to prolonged cycling at 40 °C, revealing a very stable capacity of about 140 mAh g(-1) and retention above 99 % over 400 cycles. The electrode/electrolyte interface is further characterized through a combination of electrochemical impedance spectroscopy (EIS) and scanning electron microscopy (SEM) investigations upon cell cycling. The remarkable performances reported here definitively indicate that IL-based lithium ion cells are suitable batteries for application in electric vehicles.

The performance of ionic liquid (IL) electrolytes based on N-alkyl-N-ethylpyrrolidinium cations combined with different lithium salts has been used for the design of safer lithium battery systems. These mixtures of ILs, synthesized through an eco-friendly procedure route, and salts were studied and their performance was compared on the basis of anion species. The N-butyl-N-ethylpyrrolidinium bis (fluorosulfonyl) imide/lithium bis(fluorosulfonyl) imide (PYR24FSI-LiFSI) mixture was found to exhibit superior characteristics in terms of ion transport properties even at low temperatures in combination with wide electrochemical stability, feasibility of reversibly plating lithium metal without any reduction of electrolyte and good compatibility with Li anode. These are considered to be due to good film-forming ability of the FSI anion. Conversely, lower thermal stability was also observed. Preliminary tests in lithium/lithium iron phosphate, Li/LiFePO4, half-cells using PYR24FSI-LiFSI as the electrolyte evidenced cycling performance approaching that in organic electrolytes with high capacity retention and efficiency values. (C) 2016 Elsevier Ltd. All rights reserved.

Room-temperature rechargeable sodium-ion batteries (SIBs), in view of the large availability and low cost of sodium raw materials, represent an important class of electrochemical systems suitable for application in large-scale energy storage. In this work, we report a novel, high power SIB formed by coupling the layered P2-Na0.7CoO2 cathode with the graphite anode in an optimized ether-based electrolyte. The study firstly addresses the electrochemical optimization of the two electrode materials and then the realization and characterization of the novel SIB based on their combination. The cell represents an original sodium rocking chair battery obtained combining the intercalation/de-intercalation processes of sodium within the cathode and anode layers. We show herein that this battery, favored by suitable electrode/electrolyte combination, offers unique performance in terms of cycle life, efficiency and, especially, power capability.

LiMnPO4 is an attractive cathode material for the next-generation high power Li-ion batteries, due to its high theoretical specific capacity (170 mA h g(-1)) and working voltage (4.1 V vs Li+/Li). However, two main drawbacks prevent the practical use of LiMnPO4: its low electronic conductivity and the limited lithium diffusion rate, which are responsible for the poor rate capability of the cathode. The electronic resistance is usually lowered by coating the particles with carbon, while the use of nanosize particles can alleviate the issues associated with poor ionic conductivity. It is therefore of primary importance to develop a synthetic route to LiMnPO4 nanocrystals (NCs) with controlled size and coated with a highly conductive carbon layer. We report here an effective surface etching process (using LiPF6) on colloidally synthesized LiMnPO4 NCs that makes the NCs dispersible in the aqueous glucose solution used as carbon source for the carbon coating step. Also, it is likely that the improved exposure of the NC surface to glucose facilitates the formation of a conductive carbon layer that is in intimate contact with the inorganic core, resulting in a high electronic conductivity of the electrode, as observed by us. The carbon coated etched LiMnPO4-based electrode exhibited a specific capacity of 118 mA h g(-1) at 1C, with a stable cycling performance and a capacity retention of 92% after 120 cycles at different C-rates. The delivered capacities were higher than those of electrodes based on not etched carbon coated NCs, which never exceeded 30 mA h g(-1). The rate capability here reported for the carbon coated etched LiMnPO4 nanocrystals represents an important result, taking into account that in the electrode formulation 80% wt is made of the active material and the adopted charge protocol is based on reasonable fast charge times.

A binder-free graphene anode for Li-ion batteries showing a reversible specific capacity of ∼500 mA h g−1after 100 cycles is demonstrated.

Graphene showcases several key properties that can address emerging technological needs, in particular for the storage of energy in the ever-growing market of portable and wearable electronic devices.[1] The challenge is now to develop high quality graphene flakes in large volumes to ultimately suit the needs of an industrial-scale production.[2] Liquid-phase exfoliation (LPE) of graphite [3] is emerging as a promising tool for mass production of graphene flakes, which can be prepared in the form of inks.[4,5] In particular, graphene produced by LPE is being considered a promising material for anode in Li-ion battery.[6,7] Here we report the fabrication of graphene-based anodes by LPE of graphite in NMethyl2pyrrolidone (NMP). This method allows us to obtain graphene flakes with controlled morphological properties of single layer (SLG) and few layers (FLG) graphene flakes with lateral size of ~100nm (Fig a). A solvent exchange process is used to remove the NMP and re-disperse the flakes, at a higher concentration (5g/l), in ethanol. We then formed a graphene film by drop-casting the graphene flakes at ambient conditions on a copper foil, without any binder or conductive agents, typically used in conventional LIBs. The electrochemical tests of SLGand FLG-based anodes in a half-cell configuration demonstrate a reversible specific capacity of ~ 500 mAh g -1 after 100 cycles at a current density of 100 mA g -1 , with coulombic efficiency >99.5% (Fig b). More importantly, the as-produced SLGand FLG-based anode is assembled in a full-cell configuration with commercial LiNi0.5Mn1.5O4 (LNMO) as cathode. The full cell shows promising electrochemical results, such as very high flat-plateau voltage profile at 4.7 V and a reversible specific capacity of ~100 mAh gLNMO -1 . Hence, our work successfully achieved an advanced method for graphene based electrodes fabrication, with advantages of fast deposition, low cost and scalable production method. Our process opens the way to enhance the specific capacity, energy densities, lifetime and safety of LIBs, as well as minimize their cost and environmental impacts. References [1] F. Bonaccorso et al. Science 347 1246501, 2015 [2] F. Bonaccorso et al., Mater. Today 15, 564, 2012 [3] Y. Hernandez et al. Nat.Nano 9 563, 2008 [4] F. Torrisi et al. ACS Nano 4 2992, 2012 [5] A. Capasso et al. Solid State Comm. 224, 53, 2015 [6] J. Hassoun et al. Nano Lett. 14 4901, 2014 [7] H. Sun et al. J. Mater. Chem. A DOI:10.1039/c5ta08553e 2016