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Various polyvinylidene difluorides (PVDF) as polymeric binding agent in lithium-ion battery were rheologically evaluated on high capacity and excess lithium-LiNi0.6Mn0.2Co0.2O2 (Ni-rich NMC). We found that the suspension polymerized PVDF binder is more stable upon gelation for long duration while other high molecular weight PVDF binders (MW > 900,000) show irreversible rheological transformation that can dramatically compromise the coating step during lithium-ion battery electrode slurry preparation. POLYM. ENG. SCI., 2016. © 2016 Society of Plastics Engineers

Water-soluble CMC/PVDF binder systems were used to prepare graphite anodes and compared mechanically and electrochemically with CMC/SBR binder systems. The effect of crystallinity of PVDF binder on the mechanical and electrochemical performance of the anodes is studied. A contact free method easy to operate and equipped with high accuracy was developed by using capacitance measurement. The swelling of graphite electrodes was controlled and showed different results for different binder crystallinities (no swelling of binder with high crystallinity vs 12% for medium crystallinity and 17% for low crystallinity binder). The discharge capacity depends on the crystallinity of the binders and half-cells delivered a capacity in the range of 230–360 mAh g−1. The binder with medium crystallinity in particular exhibited the best mechanical and electrochemical performance and showed an excellent C-rate stability with specific capacities up to 10 C. Full cell tests showed good cycling stability over 180 cycles. The water-based PVDF binders seem to be a promising alternative to solvent-based binders.

Bucky gel actuators are one of the most promising type of electrochemical actuators based on carbon nanotubes (CNTs). They are lightweight, they are able to work in air without any liquid electrolyte and require just few volts to operate. In order to find real world applications where bucky gel actuators can outperform conventional motors, there are still some issues to be addressed. One key aspect in CNT-based electrochemical actuators is that their actuation speed is limited by the ability of charging and discharging the device without exceeding the electrochemical stability window of the electrolyte. This speed is macroscopically related with the product of the resistance and the capacitance of the equivalent circuit (circuit time constant), and with the ion diffusion speed inside the active electrodes. To enhance the actuator performance it is necessary to increase the ion drift current in the electrolyte avoiding to significantly raise the voltage at the electrodes and shorten the ion path necessary to charge the bucky gel electrodes. By proper material processing, we have successfully addressed this issue. A reduced thickness of the actuators to one third of the original size results in a one order of magnitude increase both of the strain at higher frequencies and of the maximum operating frequency.

The study of the complex interfaces between organic semiconductors and liquids have recently gained increasing attention due to their interesting applications as biosensors in biological environments, in photovoltaics, and in bioinspired light-harvesting systems. Here, we report a detailed characterization of the interface between polymer films and electrolytic solutions, both by photocurrent spectroscopy and electrochemical measurements. In particular, we demonstrate that a photocatalytic semi-water splitting reaction, leading to hydrogen evolution, occurs at the polymer surface, directly contacted to an aqueous saline (NaCl) solution, as a consequence of visible-light generated photocurrent. We propose here a fully unexplored application of organic systems, i.e. the development of fuel cells: our results pave the way to the exploitation of organic polymers, seawater and solar energy as the sole raw materials for completely clean, sustainable, and economical hydrogen production.

Bucky gel-based actuators represent one of the possible ways to exploit the outstanding electrical and mechanical properties of carbon nanotubes. Despite the continuous efforts to develop better devices, the lack of an accepted and simple way of characterizing the actuation mechanisms has often led to misestimate their performances. In this paper we examine some of the main works in literature on this subject, in order to reconsider the proposed actuation models in terms of purely material-dependent parameters instead of geometry-dependent ones. Applying the promoted approach, we demonstrate how proper cross-linking treatments on carbon nanotubes endow bucky gel actuators with superior performance.

Chemical cross-linking of super-growth carbon nanotubes was performed to increase bucky gel actuators efficiency in transferring motion from the nano-scale to the micro-scale. The modification was achieved by a three-step reaction i.e. first an oxidation with nitric acid, then a chlorination process with thionyl chloride and finally the cross-linking with an aromatic diamine. The use of cross-linked nanotubes in bucky gel results in a threefold increase of the charge transfer capability of the composite material and an increase up to ten times of the strain generated by the resulting actuators. To our knowledge, such bucky gel actuators, prepared using cross-linked super growth carbon nanotubes, outperform any other electrochemical carbon nanotube actuator presented so far.

Both carbon nanotubes (CNTs) and polypyrrole (PPy) have been investigated as materials for manufacturing high charge-transfer electrodes due to their outstanding performances. The combination of their complementary properties via an electrochemical co-deposition route has been already shown to achieve interesting results. In this work, PPy and chemically-functionalized multi walled CNTs (COOH-MWCNT) were potentiostatically, galvanostatically and potentiodynamically electrodeposited from an aqueous solution to form a nanocomposite on the surface of a variety of metal electrodes. A study of the influence of experimental parameters such as temperature, current, and growth rate in the different electrodeposition methods was performed. The electronic and electrochemical properties of the nanocomposite films have been studied by cyclic voltammetry and electrochemical impedance spectroscopy, while a morphological study has been performed via scanning electron microscopy. A comparison between the different techniques and guidelines for best results will be reported.

Carbon nanotubes (CNTs) have electrical and mechanical properties that make them highly attractive for actuators. They have the ability to deform elastically by several percent, thus storing very large amounts of energy, thanks to their crystalline nature and to their morphology. A bimorph actuator composed of single-walled carbon nanotubes (SWCNTs), polyvinylidene difluoride (PVdF) and the ionic liquid (IL) 1-butyl 3-methylimidazolium tetrafluoroborate [BMIM][BF 4 ] with a polymer-supported internal IL electrolyte was previously demonstrated by Aida and coworkers. While several experiments were carried out using SWCNTs, PVdF and a number of ILs, the use of multi-walled carbon nanotubes (MWCNTs) instead of SWCNTs is, to our knowledge, a new result that will be presented here. Electrochemical characterizations by cyclic voltammetry (CV), and actuation tests performed applying a square wave of 4 V peak-to-peak at frequencies between 0.3 and 2 Hz are reported and discussed.

Passive direct methanol fuel cells (DMFCs) are considered interesting candidates for small-scale power applications. We investigated the performance in passive DMFCs of the PtRu catalyst supported on poly(3,4-ethylenedioxythiophene)-polystyrene-4-sulfonate (pEDOT-pSS), a Nafion-free, mixed electronic-protonic conductor that assures electronic transport for methanol oxidation at the anode and provides the proton movement. The DMFCs were assembled with Vulcan XC-72R carbon/Pt (in excess) cathode, Nafion 117 membranes and 1 M CH3OH, and long-time performance data are reported and discussed.

In this paper, we propose a novel technological approach for the implementation of large-area flexible artificial skin based on arrays of piezoelectric polymer transducers. Polyvinylidene fluoride (PVDF) transducers are chosen for the high electromechanical transduction frequency bandwidth (up to 1 kHz). A low-cost and scalable technique for extracting PVDF signals is used to directly provide the piezoelectric film with patterned electrodes. If the skin is meant to cover large areas of a robot body, specific requirements have to be fulfilled from the point of view of the overall system and of the technology. Experimental tests on the prototype skin modules demonstrate the feasibility of the proposed approach and reveal the potentiality to build large area flexible skin.

Single walled carbon nanotubes functionalized with an aromatic diamine have been successfully used to prepare bucky gel layers by mixing with an imidazolium based ionic liquid, allowing to build bimorph actuators that significantly outperform those prepared by using the pristine or oxidized carbon nanotubes. The carbon nanotube gravimetric specific capacitance doubles, the actuator maximum operating frequency becomes five times higher and for same injected charge the strain reaches a fourfold increase. The origin of such dramatic effects is most probably due to an enhanced binding between the carbon nanotubes induced by their chemical modification. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Low voltage, dry electrochemical actuators can be prepared by using a gel made of carbon nanotubes and ionic liquid. 1 Their performance can be significantly improved by combining physical and chemical modifications with a proper engineering. We demonstrated that multi walled carbon nanotubes can be effectively used for actuators preparation; 2 we achieved interesting performance improvements by chemically cross linking carbon nanotubes using both aromatic and aliphatic diamines; 3 we introduced a novel hybrid material, made by in-situ chemical polymerization of pyrrole on carbon nanotubes, that further boosts actuation by taking advantage of the peculiar properties of both materials in terms of maximum strain and conductivity; 4 we investigated the influence of actuator thickness showing that the generated strain at high frequency is strongly enhanced when thickness is reduced. To overcome limitations set by bimorphs, we designed a novel actuator in which a metal spring, embedded in the solid electrolyte of a bimorph device, is used as a non-actuating counter plate resulting in a three electrode device capable of both linear and bending motion. Finally, we propose a way to model actuators performance in terms of purely material-dependent parameters instead of geometry-dependent ones. 5

New polyaniline (PANi) synthesis was performed starting from non-toxic N-phenil-p-phenylenediamine (aniline dimer) using reverse addition of monomer to oxidizing agent, the synthesis allows to produce highly soluble PANi. Several types of doped PANi were prepared to be used on electromechanical active actuators. Different techniques were used to include carbon nanoparticles such as carbon nanotubes and graphene. Bimorph solid state ionic actuators were prepared with these novel nanocomposites using a variety of supporting polymers.

Oxidative polymerization of pyrrole directly on preformed bucky gel slurry was carried out in order to combine the remarkable properties of ionic actuators based on carbon nanotubes and polypyrrole. Bimorph solid state ionic actuators were prepared with this novel hybrid material and compared with classical bucky gel actuators. A small amount of polypyrrole is sufficient to dramatically improve the overall actuator performance. The maximum strain is five times larger than the one of actuators prepared only with carbon nanotubes. Moreover, for the same applied charge, the strain generated increases up to twenty-five times.

Humanoid robots use tactile fingertips to perform object manipulation. In this paper, an improved prototype of a tactile capacitive fingertip for the hands of the humanoid robot iCub is presented. In particular, a conductive silicone based material has been used to improve the characteristics of the capacitive sensor and an additional silicone foam layer has been also introduced in the sensor architecture to prevent behavior variation due to fingertip deterioration (e.g., caused by object manipulation). A characterization of the fingertip sensing behavior is presented. This work is funded by the European Commission as part of the project ICT-FP7-231500 RoboSKIN.

In 2003 Takuzo Aida and coworkers reported that single-walled carbon nanotubes (SW-CNTs), when ground with imidazolium based ionic liquids (ILs), create a physical gel, named "bucky gel" 1 . This gel was used to prepare bimorph electrochemical actuators using a polymer-supported internal IL electrolyte layer 2 . These actuators can operate in air at low voltage showing improved frequency response and strain. Usual bucky gel actuators rely on a bimorph configuration where the electrodes are used alternatively as cathode and anode thus producing a bending motion. This kind of motion is limiting the possible applications, especially when, like in artificial muscles, linear strain and motion are required. We present a new design for bucky gel actuators capable of both linear and bending motion that uses a three electrode configuration with two active electrodes and a third passive one, made from a metal spring (serpentine shaped), acting as counter plate. We have built such a device and report here its linear and bending actuation performance. In these preliminary experiments we have obtained a linear strain of 0.6% and a bending strain difference between two bucky gel electrodes of 0.25%.

Bucky gels are considered novel electro active polymers based on carbon nanotubes (CNTs). They are used to make electrochemical actuators that operate with a solid polymer electrolyte and so can work in air at low voltage (2–4 V) for long time with a maximum strain of approximately 1% and operating frequencies of a few tens of Hertz. It is reported in literature that the use of super-growth carbon nanotubes (SG-CNTs) affords the preparation of a composite with increased actuation performance that may considered the ‘benchmark’ material. We have recently shown a chemical route to modify single walled carbon nanotubes (SW-CNTs) with aromatic diamines (SW-amide) that significantly enhances the performance of bucky gel actuators through increasing the binding between CNTs. In this paper we compare the actuation performance of bucky gels made using chemically modified SW-CNTs with the one achieved using pristine SG-CNTs. The unique properties of SG-CNTs allow the preparation of actuators that outperform the ones made from pristine commercial CNTs in strain-charge and strain-frequency response but when SW-amide based actuators are compared with those made from SG-CNTs they show similar performances that stem from the increased binding between CNTs induced by the chemical modification.

doi: 10.1016/j.jowsour.2008.09.016 Safety is the main concern for energy storage-system application in hybrid-electrical vehicles (HEVs) and ionic liquids (ILs) of low vapour pressure and high thermal stability represent a strategy to meet this key requisite. The use of solvent-free ILs in supercapacitors enables the high cell voltages required for increasing supercapacitor energy up to the values for power-assist application in HEVs. In order to exploit the wide electrochemical stability window of ILs, tailored electrode materials and cell configurations have to be used. The performance of asymmetric double-layer carbon supercapacitors (AEDLCs) and carbon/poly(3-methylthiophene) hybrid supercapacitors operating with different pyrrolidinium-based ILs are reported and compared. This study demonstrates that a design-optimized AEDLC operating with safe, solvent-free IL electrolyte meets cycling stability and the energy and power requisites for power-assisted HEVs at the investigated temperatures.

The ionic liquids (ILs) N-butyl-N-methyl-pyrrolidinium trifluoromethanesulfonate (PYR14Tf) and N-methyl-N-propyl-pyrrolidinium bis(fluorosulfonyl)imide (PYR13FSI) are investigated as electropolymerization media for poly(3-methylthiophene) (pMeT) in view of their use in carbon/IL/pMeT hybrid supercapacitors. Data on the viscosity, solvent polarity, conductivity and electrochemical stability of PYR14Tf and PYR13FSI as well as the effect of their properties on the electropolymerization and electrochemical performance of pMeT, which features >200 Fg−1 at 60 °C when prepared and tested in such ILs, are reported and discussed; the results of the electrochemical characterization in N-butyl-N-methyl-pyrrolidinium bis(trifluoromethanesulfonyl)imide of the so-obtained pMeT are also given, for comparison.

Li-ion batteries are widely used in a large number of devices that are used in everyday life, from Smart Devices to Hybrd Electric Vehicles (HEVs). The research is prompted towards the development of innovative materials that can further enhance the performances of batteries1,2. Research on anodic materials is of crucial importance to meet the requirements for cited applications in terms of power and energy density. On this side, Silicon is considered to be the most promising material in terms of deliverable theoretical specific capacity, 4200 mAh/g. However, cycling performances of Silicon are jeopardized by the structural instability suffered from the material upon charge/discharge cycling. To address this issue, different solutions have been tested3 , 4. The approach developed in this work is to apply a metallic coating to the Si particles by electrochemical techniques, i.e. electroless deposition and galvanic displacement. In this work, a study of the electrochemical impact of the coating on the behavior of the electrode will be done in two steps. First, an assessment of the growth mechanism of metallic coating on Si particles will be carried out by means of SEM analysis. Then, the electrochemical characterization of electrodes containing metallized particles will be carried out by means of electrochemical impedance spectroscopy, SEM analysis and coin cell cycling. References: 1. J. B. Goodenough and Y. Kim, Chem. Mater., 22, 587–603 (2010) 2. Y. Sun et al., Nat. Mater., 11, 942–947 (2012) 3. C. K. Chan et al., Nat. Nanotechnol., 3, 31–5 (2008) 4. B. A. Boukamp, J. Electrochem. Soc., 128, 725 (1981)

Silicon is a material that has gained particular interest for the application as anode active material in lithium ion batteries, thanks to its unique reversible lithium insertion capability, which can lead to very high values of specific capacity. However, the main drawback that prevented the spreading of this material in industrial application is its structural instability upon lithium insertion cycling, and different solution have been proposed to address this issue 1 , 2. The very high volume variation that occurs to silicon during cycling leads to difficulty to establish a continuative electrical contact between Si particles and the rest of the electrode. The approach developed in this work is to apply a nanostructured metallic coating to the Si particles, helping to overcome the continuous stresses during cycling and maintaining electrical contact. In this work, two different metallization techniques have been tested. The presence and composition of the coating on the surface of the particles is confirmed by SEM/EDX and XRD analysis. Anodes containing at least 20%wt Si have been manufactured to perform the electrochemical characterization and to assess the cycling behavior. Coated particles show enhanced structural stability upon cycling, leading to improved cycling efficiency and cycle life. Specific capacity values around 1000 mAh/g are achieved with a 40% increase with respect to pristine Si. References: 1. C. K. Chan et al., Nature nanotechnology, 3, 31–35 (2008). 2. B. A. Boukamp, Journal of The Electrochemical Society, 128, 725 (1981).

Bucky gel actuators are a kind of electrochemical actuator based on carbon nanotubes having interesting features. They are intrinsically safe because are operated at low voltage, they are lightweight and they are able to work in air without any liquid electrolyte. One key aspect that needs improvement is their actuation speed which is strongly dependent on their ability of being efficiently charged and discharged without exceeding the electrochemical stability window of the electrolyte. By proper material processing, we have successfully addressed this issue. An actuator thickness reduction to one third of the original size results in a one order of magnitude increase of both the strain at higher frequencies and the maximum operating frequency. The strain improvement at high frequency due to thinning has the sole drawback of decreasing the maximum strain that can be achieved in quasi-static conditions. We addressed this second issue by using a proper combination of actuating materials. Oxidative polymerization of pyrrole was carried out directly on preformed bucky gel slurry in order to combine the remarkable properties of ionic actuators based on carbon nanotubes and polypyrrole. A small amount of polypyrrole is sufficient to dramatically improve the overall actuator performance, and by using this hybrid it is possible to obtain thin actuators (about 0.1 mm) with superior performance even at lower frequencies.

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Object grasping and manipulation in humanoid robots depend, for advanced and long lasting performance, on the development of reliable tactile sensors. Materials used for sensor implementation have to be chosen accurately and optimized in order to endow the device with sufficient resilience to endure long lasting grasping tasks. In particular care has to be taken when trying to enhance durability by the use of materials with high shore hardness as this choice can noticeably reduce pressure sensitivity. In this paper, a comparison between two implementations of the fingertip sensor of the humanoid robot iCub is presented by using a raw characterization of the response along a straight line. Prototypes differ in the materials used for the dielectric and protective layers, while maintaining the same capacitive architecture. The relevant result that emerges from the characterization is that the prototype with Soma Foama presents a higher sensitivity compared to the prototype in PDMS, while the second has a higher mechanical strength.