Broadband Electrical Spectroscopy Research Articles

(Invited) Overview of Ionic Liquid Electrolytes Doped with δ-Metal Halides for Advanced Post-Lithium-Ion Batteries

Humankind is currently facing a global transition towards a green electrification of both energy production and transportation. There is an urgent need to find new approaches for the storage of energy derived from renewable sources, such as solar irradiation, wind and waves. In addition, electric cars require energy storage or conversion systems capable of providing engine power. To these ends, secondary batteries are an attractive and viable solution, especially in the form of the relatively mature Li-ion technology. Unfortunately, Li power sources suffer from high cost, low Li earth-crust abundance, and toxicity of their electrochemical components (e.g., the Co-based cathodes). Such disadvantages demand the exploration of new energy storage devices based on alternative chemistries (e.g., Na, Mg, Ca).Since their discovery [1-5], electrolytes based on disordered or delta metal halide salts (e.g., δ-MgCl2, δ-LiCl, δ-MgI2) have received widespread attention due to their intriguing physical-chemical properties. Subsequently, electrolytes comprised of ionic liquid solvents dispersing various δ-metal halide salts were investigated [6-9]. These latter ion-conducting systems are characterized by: (i) very high room-temperature ionic conductivity; (ii) wide thermal, chemical and electrochemical stability; and (iii) high coulombic efficiency and very low overpotentials in the metal deposition and stripping processes.In this contribution, a comparison of different families of ionic liquids will be proposed. In particular, the effects of the use of δ-metal halide salts (e.g., δ-MgCl2, δ-LiCl, and δ-NaCl) on the thermal stability, vibrational features, and electrochemical properties of the resulting electrolytes will be considered. The conductivity mechanisms will be analyzed side-by-side, revealing how ionic conductivity is modulated by the metal ions (e.g., Mg2+, Li+, Na+), on the basis of broadband electrical spectroscopy results. Acknowledgments The authors acknowledge support in the form of the following grants: project “Interplay between structure, properties, relaxations and conductivity mechanism in new electrolytes for secondary Magnesium batteries” (Grant Agreement W911NF-21-1-0347-(78622-CH-INT)) of the U.S. Army Research Office; project “ACHILLES” (prot. BIRD219831) of the University of Padua; project “VIDICAT” (Grant Agreement 829145) of the FET-Open call of Horizon 2020; project “Polymer electrolytes for Sodium Batteries” (Grant Agreement 72957-00 01) sponsored by Natrion Inc. and the CUNY Sensor CAT.

(Invited) Solid State Hybrid Inorganic Organic Polymer Electrolytes for Advanced Sodium Secondary Batteries

The large-scale rollout of electric vehicles, smart grids and portable electronics is expected to require an amount of energy storage devices that the Li-ion technology alone will not be able to satisfy. In this concern, a quest for novel electrochemical energy storage technologies has started [1]. Sodium secondary batteries appear to be a good choice due to: (i) the high availability of raw materials; (ii) the low cost of sodium; (iii) the low sodium standard reduction potential; and (iv) the similarity between the chemistries of sodium and lithium, which facilitates the transition between the two technologies. Up to date, the best-performing electrolytes for the reversible deposition of sodium are based on organic solvents, which suffer from safety concerns and a poor stability towards sodium metal. Thus, research activities in this field are devoted to the development of safe and stable solid state electrolytes able to efficiently transport Na+ ions.Inspired by the pioneering work done by Di Noto and co-workers [2-4], herein we present a family of hybrid inorganic-organic polymer electrolytes (HIOPEs) for advanced solid state sodium secondary batteries. The initial HIOPE is obtained by means of a reaction between zirconium ethoxide and polyethylene glycol (PEG400). The resulting material is doped with sodium perchlorate as source of Na+ ions. In this system a 3D network is obtained, where inorganic zirconium metal nodes are interconnected by means of organic PEO chains. The latter ensure flexibility to the overall structure. Na+ ions are coordinated by and exchanged between the oxygen atoms of the ethereal functionalities of PEO chains. In addition, to guarantee a good structural stability, positively charged Zr nodes partially coordinate perchlorate anions, thus raising the sodium transference number. After doping with the poly(ethylene glycol) dimethyl ether (PEGDME250) plasticizer, a room temperature conductivity higher than 10-4 S cm-1 is demonstrated. An advanced study of the thermal and structural properties of the proposed materials is presented, with a particular focus on the interactions established between the different chemical species and complexes composing the HIOPEs. The conduction mechanism is elucidated starting from the results obtained in a wide range of temperatures from broadband electrical spectroscopy studies. Taking all together, this study offers insights on the application of non-traditional solid state electrochemical functional components as replacements for conventional solvents in the emerging field of sodium secondary batteries. Acknowledgments The project “Interplay between structure, properties, relaxations and conductivity mechanism in new electrolytes for secondary Magnesium batteries” (Grant Agreement W911NF-21-1-0347-(78622-CH-INT)) of the U.S. Army Research Office. The project “ACHILLES” (prot. BIRD219831) of the University of Padua. The project “VIDICAT” (Grant Agreement 829145) of the FET-Open call of Horizion 2020. The project TRUST (protocol 2017MCEEY4) of the Italian MIUR funded in the framework of “PRIN 2017” call.

Broadband Electrical Spectroscopy to Distinguish Single-Cell Ca2+ Changes Due to Ionomycin Treatment in a Skeletal Muscle Cell Line.

Many skeletal muscle diseases such as muscular dystrophy, myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS), and sarcopenia share the dysregulation of calcium (Ca2+) as a key mechanism of disease at a cellular level. Cytosolic concentrations of Ca2+ can signal dysregulation in organelles including the mitochondria, nucleus, and sarcoplasmic reticulum in skeletal muscle. In this work, a treatment is applied to mimic the Ca2+ increase associated with these atrophy-related disease states, and broadband impedance measurements are taken for single cells with and without this treatment using a microfluidic device. The resulting impedance measurements are fitted using a single-shell circuit simulation to show calculated electrical dielectric property contributions based on these Ca2+ changes. From this, similar distributions were seen in the Ca2+ from fluorescence measurements and the distribution of the S-parameter at a single frequency, identifying Ca2+ as the main contributor to the electrical differences being identified. Extracted dielectric parameters also showed different distribution patterns between the untreated and ionomycin-treated groups; however, the overall electrical parameters suggest the impact of Ca2+-induced changes at a wider range of frequencies.

Catenated pyrrolidinium-magnesium-organochlorostannate ionic liquid electrolytes for multivalent metal batteries

The quest for the development of high performing secondary batteries is prompting the research activities in this field towards the exploitation of new cell concepts. In this concern, next-generation secondary batteries based on multivalent metals such as magnesium and tin are an important promise. In this report, a new family of multivalent metal-based ionic liquid (IL) electrolytes is developed. The proposed ILs are obtained by reacting 1-butyl-1-methylpyrrolidinium chloride (Pyr14Cl), dimethyl-tin dichloride and the highly electroactive δ-MgCl2 material. Thermal and vibrational spectroscopy studies reveal that the proposed electrolytes consist of domains of complex catenated 3D magnesium-organochlorostannate coordination networks neutralized by aggregates of Pyr14+ stacks. The anionic domains are composed by a network of catenated [Me2xSnxCl2x+y]y− repeat units bonded by MgClx bridges. Cyclic voltammetry studies reveal that the metal deposition and stripping processes occur with a low overpotential in the order of few tens of mV. Finally, broadband electrical spectroscopy studies show that these new IL electrolytes: (i) are characterized by a room temperature ionic conductivity in the order of 10−3 S cm−1; and (ii) exhibit host matrix relaxations which are very effective in facilitating the long-range charge migration processes responsible for the overall conductivity of materials.

Quantum view of Li-ion high mobility at carbon-coated cathode interfaces

Lithium-ion batteries (LIBs) are among the most promising power sources for electric vehicles, portable electronics and smart grids. In LIBs, the cathode is a major bottleneck, with a particular reference to its low electrical conductivity and Li-ion diffusivity. The coating with carbon layers is generally employed to enhance the electrical conductivity and to protect the active material from degradation during operation. Here, we demonstrate that this layer has a primary role in the lithium diffusivity into the cathode nanoparticles. Positron is a useful quantum probe at the electroactive materials/carbon interface to sense the mobility of Li-ion. Broadband electrical spectroscopy demonstrates that only a small number of Li-ions are moving, and that their diffusion strongly depends on the type of carbon additive. Positron annihilation and broadband electrical spectroscopies are crucial complementary tools to investigate the electronic effect of the carbon phase on the cathode performance and Li-ion dynamics in electroactive materials.

(Invited) A New Frontier in Hybrid Inorganic-Organic Membranes for Redox Flow Batteries: The Polyketone-Based Membranes

Zinc iodide flow batteries (ZIFBs) are amongst the most promising chemistries to substitute the expensive and less energy intensive Vanadium Flow Batteries (VFBs). One of main problems related to this technology is the crossover of water due to the transport of Zn2+. One possible approach is the development of new ion-exchange membranes (IEMs). For practical applications they are required to possess high ionic conductivity, high thermal stability, long lifetime, and electrical insulation. The preparation of polymeric materials with such high-performance properties is still challenging and can lead to high prices, hindering their widespread use in energy conversion technologies. This is even more difficult when considering anion conducting membranes [1-3].Polyketones (PK) are known to be high performance thermoplastic polymers with applications ranging from fire-retardants film coatings, packaging, and fibers, resulting from their high thermal and chemical stability. They can be obtained in high yields by copolymerization of inexpensive and readily available feedstocks such as ethylene and carbon monoxide. Our group proved that PK with alternating 1,4-dicarbonyl repeating units constitute an ideal starting point to access a wide class of modified polymers by simple Paal-Knorr cyclization, to gain pyrrole-N-bound functional groups stemming from the aliphatic backbone [4-5].Different ion-conducting membranes have been developed and the effect of reaction conditions on their thermal properties, chemical stability, and their conductivity in a wide range of frequencies have been assessed by broadband electric spectroscopy to shed light on the conduction mechanisms [4, 6]. The more promising material developed has been tested in a single cell redox flow battery obtaining promising results.The proposed conducting polymers combine the thermal stability of the aliphatic PK structure with the chemical flexibility given by the groups derived from functionalized amines branching out, proving to be highly tailorable, with possible applications in current energy conversion technologies. Acknowledgements: The authors wish to thank the Research Projects of Relevant National Interest (PRIN 2017) of the Italian Ministry of Education, University and Research “Novel Multilayered and Micro-Machined Electrode Nano-Architectures for Electrocatalytic Applications (Fuel Cells and Electrolyzers)” (Prot. 2017YH9MRK) and SID2020 Project of Department of Industrial Engineering, University of Padova “A New frontier in Hybrid Inorganic-Organic Membranes for Energy Conversion and Storage Devices” (Prot. BIRD201244) for funding.

Magnesium- and Tin-Based Ionic Liquid Electrolytes for Advanced Multivalent Metal Batteries

In the recent years, the global energy economy is experiencing a transition towards its production from more sustainable and “green” sources. The intrinsic characteristics of these methods, such as the intermittency and misalignment between disposability and demand, require the use of energy storage systems, such as secondary batteries. Despite the high performance of Li-ion batteries, the high cost, low abundance and toxicity of their components (e.g., the Co-based cathodes) request the development of new devices based on novel chemistries. In this regard, the holy grail is the production of battery systems based on abundant multivalent metals.It has been recently demonstrated that ionic liquids (ILs) are suitable solvents in order to obtain stable and high performing electrolytes able to conduct and deposit/strip multivalent metals [1-5]. The outstanding electrochemical properties of these materials are ensured by the presence of a high-reactive magnesium salt (i.e., the “delta” form of MgCl2) and of a suitable metal halide (e.g., AlCl3, TiCl4, etc.). In this project we have developed a family of IL-based electrolytes for the Mg2+ ion conduction doped with an alkyl tin halide compound. In this way, the hybrid chemico-physical properties of Sn-based species can be exploited to improve the coordination existing between the inorganic magnesium salt and the organic IL. An advanced study on the thermal and structural properties of the proposed material will be presented, with a particular focus on the interactions established between the different chemical species and complexes composing the materials. Insights on the conductivity mechanism occurring in a wide range of temperature will be gauged and thoroughly described by means of the broadband electrical spectroscopy studies. Acknowledgments The project “Interplay between structure, properties, relaxations and conductivity mechanism in new electrolytes for secondary Magnesium batteries” (Grant Agreement W911NF-21-1-0347-(78622-CH-INT)) of the U.S. Army Research Office. The project “ACHILLES” (prot. BIRD219831) of the University of Padua. The project “VIDICAT” (Grant Agreement 829145) of the FET-Open call of Horizion 2020.

Effect of Relaxations on the Conductivity of La1/2+1/2x Li1/2-1/2x Ti1-x Al x O3 Fast Ion Conductors.

Perovskite-type solid-state electrolytes, Li3xLa2/3–xTiO3 (LLTO), are considered among the most promising candidates for the development of all-solid-state batteries based on lithium metal. Their high bulk ionic conductivity can be modulated by substituting part of the atoms hosted in the A- or B-site of the LLTO structure. In this work, we investigate the crystal structure and the long-range charge migration processes characterizing a family of perovskites with the general formula La1/2+1/2xLi1/2–1/2xTi1–xAlxO3 (0 ≤ x ≤ 0.6), in which the charge balance and the nominal A-site vacancies (nA = 0) are preserved. X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM) investigations reveal the presence of a very complex nanostructure constituted by a mixture of two different ordered nanoregions of tetragonal P4/mmm and rhombohedral R3̅c symmetries. Broadband electrical spectroscopy studies confirm the presence of different crystalline domains and demonstrate that the structural fluctuations of the BO6 octahedra require to be intra- and intercell coupled, to enable the long-range diffusion of the lithium cation, in a similar way to the segmental mode that takes place in polymer-ion conductors. These hypotheses are corroborated by density functional theory (DFT) calculations and molecular dynamic simulations.

Interplay between coordination, dynamics, and conductivity mechanism in Mg/Al-catenated ionic liquid electrolytes

The development of batteries based on alternatives to lithium is essential to sustaining the increasing global energy demand. Earth abundant, energy dense metal anodes with mixed multivalent ions (e.g., Mg/Al) are promising next-generation systems. A critical challenge, however, is the development of advanced electrolytes that are compatible with them. To achieve this target, a deeper understanding of their properties and conductivity mechanisms is needed. Herein, in a family of Al/Mg mixed metal ionic liquid-based electrolytes for secondary batteries, the ion-speciation, thermal behavior and long-range charge-migration processes is studied. It is revealed that the chemical compositions and temperature modulate the distribution of AlCl4− and Al2Cl7− species in the anionic nanoaggregates of materials. These modifications are responsible of the mobility of ions, which is studied in detail by means of broadband electrical spectroscopy and pulse-field-gradient NMR. Results yield a clear picture of the role of ion aggregates in the long-range charge-migration processes occurring in these electrolytes.

Inorganic‐Organic Hybrid Anion Conducting Membranes Based on Ammonium‐Functionalized Polyethylene Pyrrole‐Polyethylene Ketone Copolymer

AbstractNew inorganic‐organic hybrid anion exchange membranes are produced after incorporation of tantalum oxide into trimethylammonium‐functionalized polyethylene pyrrole‐co‐polyethylene ketone (functionalized polyketone, FPK), obtained by the chemical modification of a polyketone polymer. The influence of tantalum oxide fillers on the properties of the synthesized membranes is investigated. The interaction between inorganic fillers and the polymer chains is studied using Attenuated Total Reflectance Fourier Transform Infrared Spectroscopy (ATR‐FTIR). The thermal analysis of the FPK membranes reveals they are thermally stable at up to 250°C. However, the incorporation of the inorganic fillers reduces the thermal stability. Modulated Differential Scanning Calorimetry (MDSC) results indicate that the inclusion of inorganic fillers leads to an increase in crystallinity. This study reports that the properties of the bulk polymer can be tuned by controlling the degree of functionalization and content of inorganic fillers, as confirmed by Near Ambient Pressure X‐Ray Photoelectron Spectroscopy (NAP‐XPS) studies. Finally, Broadband Electrical Spectroscopy (BES) studies demonstrate that the hybrid membranes are characterized by several polarization phenomena contributing to the overall ion conductivity of the material, which at RT is of 1.46 and 1.61 mS cm−1 for the FPK cast membrane and the hybrid membrane with 5.0 wt.% of Ta2O5 filler, respectively.

The Role of Structural Features and System Relaxations on the Electrical Response of La1/2+1/2xLi1/2-1/2xTi1-XAlxO3 Perovskites

The all-solid-state batteries (ASSBs) using solid electrolytes are excellent candidates for the next generation of commercial devices for energy storage. Among these, the perovskite-type family of Li-ion conducting oxides Li3xLa2/3−xTiO3 (LLTO) is one of the most studied [1] and it is shown as the most promising option for solid electrolytes because of its high bulk conductivity (10−3 S·cm−1) [2], negligible electronic conductivity [3] high stability, wide electrochemical window (larger than 4 V) [4] and easy preparation. [5] However, there are still many challenges to be solved: (i) the high impedance associated with grain boundaries which reduce the overall lithium ionic conductivity below 10-5 S/cm at 298 K; (ii) and the instability of LLTO in direct contact with metal Li, [6],[7] or graphite electrodes.[8], [9],[10] In this contribution, we have focused on the substitution of B-site of LLTO perovskite, La1/2+1/2xLi1/2-1/2xTi1-xAlxO3 (0 ≤ x ≤ 1) studying the influence of vacancy distribution on percolative phenomena. Along this series, (1/2Li+ + Ti4+) cations were substituted by (1/2La3+ +Al3+), preserving both the charge balance and the nominal A-site vacancies (nA = 0). Accordingly, the main goal of this study is to confirm the influence of effective vacancies and their distribution, instead of nominal vacancies, on the Li conduction mechanism. The presence of order/segregation must influence the conductivity of these materials and by performing Broad band Electric Spectroscopy (BES), which is a powerful technique for unravelling the complexities of a polycrystalline ceramic, the analysis of the different contributions to the electric response of this complex materials can be achieved[11], [12].Indeed, here the aim is to study the correlation between structural features, determined by HRTEM/STEM, and relaxation phenomena characterizing the electric response of these perovskites by means of the BES. To better elucidate the interplay between structural features, conductivity and relaxation phenomena from the electric response of these materials, Density Functional Theory (DFT) and dynamic molecular modelling simulations studies are carried out.Taking all together, it is shown that the charge migration processes occurring along the different conductivity pathways for Li+ long range migration phenomena are very effective when in these perovskites: a) a sufficient density of charge carriers is present; and b) in the Ti4+ based BO6 backbone octahedra, Al3+ ions acts as a defect, thus enhancing the dynamics characterizing their relaxation modes. This latter effect is obviously dependent on the existence of an efficient coupling between the host medium relaxations of the inorganic network and the relaxation events characterizing the long range migration processes of lithium conductivity pathways.In conclusion, this study permits to shed light precisely into the conduction mechanism in Li3xLa2/3−xTiO3 –type perovskites. Acknowledgements This work has been supported by the European Union’s Horizon 2020 research and innovation program under grant agreement No 829145 (FETOPEN-VIDICAT) and by the Agencia Española de Investigación /Fondo Europeo de Desarrollo Regional (FEDER/UE) for funding the projects PID2019-106662RBC43 and C44. V. Di Noto thanks the University Carlos III of Madrid for the "Cátedras de Excelencia UC3M-Santander" (Chair of Excellence UC3M-Santander).

Correlations between Composition, Matrix Dynamics and Ca2+ Conductivity in Ca-Polyoxyethylene Polymer Electrolytes

In the last decades, the humankind is facing a radical transition towards the development of sustainable methods for the energy conversion endowed with a lower environmental impact with respect to fossil fuels. Examples are solar, wind, tides, etc., which, unfortunately, suffer from an intermittent availability and a misalignment between disposability and demand, thus requesting the coupling with energy storage devices. In addition to this, the growing market of electric vehicles is requesting more performing and lower cost batteries with respect to those based on the lithium-ion technology. In this regard, the development of novel chemistries, preferentially based on multivalent metals, is an open quest. Among the different multivalent metals, calcium can be considered a good choice, as it shows a similar theoretical volumetric capacity and reduction potential with respect to lithium (i.e., 2.06 vs. 2.06 Ah cm-3 and -3.05 vs. -2.87 V against SHE for Li and Ca, respectively) and a high abundance in the Earth’s crust [1]. The widespread of calcium batteries is mainly bottlenecked by the development of suitable Ca2+ ion-conducting materials able to deposit and strip calcium metal [1-4]. Moreover, the understanding of the coordination and exchange of Ca2+ ions in the electrolyte, and thus the conductivity mechanism, is mostly unknown, especially when a polymer matrix is used.In this work we investigate the conductivity mechanism of Ca2+-ion in polyoxyethylene (POE) solid polymer electrolytes (SPEs) for calcium secondary batteries by means of broadband electrical spectroscopy studies. Three different calcium salts are taken under consideration (i.e., CaTf2, Ca(TFSI)2 and CaI2) in order to demonstrate the role of the anion in the formation of ion-polymer host matrix interactions, and thus in the modulation of the conductivity mechanism. It is shown that the long-range charge migration processes occurring along the different percolation pathways of these systems are generally coupled with the polymer host matrix dynamics and are influenced by the temperature and the anion nature. Indeed, it is demonstrated that the anions are able to induce the formation of “dynamic crosslinks”, whose density is regulated by their different steric hindrance and charge density. Concluding, this study paves the way towards the understanding of Ca2+ conduction in POE-based electrolytes. Acknowledgements This work has been supported by the European Union’s Horizon 2020 research and innovation programme under grant agreement No 829145 (FETOPEN-VIDICAT). V. Di Noto thanks the University Carlos III of Madrid for the “Catedras de Excelencia UC3M-Santander” (Chair of Excellence UC3M-Santander).

Polyketone Functionalization: New Ways to Anion Conducting Polymers

Ion-exchange membranes (IEMs) are at the core of many energy storage and conversion devices, such as fuel cells and redox flow batteries, being responsible for the migration of ionic species, separating the fuel stocks, and providing support to the electrode assemblies. For practical applications they are required to possess not only high ionic conductivity, but also specificity, thermal stability, long lifetime, and electrical insulation. The preparation of polymeric materials with such high-performance properties is still challenging and can lead to high prices, hindering their widespread use in energy conversion technologies. This is even more arduous when considering polymers to be used in anion conducting membranes, due to the need for the extra chemical stability and ability to withstand alkaline conditions at high temperatures for long periods of time [1].Polyketones are known to be high performance thermoplastic polymers with applications ranging from fire-retardants film coatings, packaging, and fibers, resulting from their high thermal and chemical stability. They can be obtained in high yields by copolymerization of inexpensive and readily available feedstocks such as ethylene and carbon monoxide. Our group proved that polyketones with alternating 1,4-dicarbonyl repeating units constitute an ideal starting point to access a wide class of modified polymers by simple Paal-Knorr cyclization, to gain pyrrole-N-bound functional groups stemming from the aliphatic backbone [2].This is a new account on our research on the ion conducting polymeric materials derived from polyketone, obtained by reaction with variously functionalized amines, and their easy conversion to anion exchange materials. The effect of reaction conditions on their thermal properties and chemical stability in alkaline media has been studied, and their conductivity in a wide range of frequencies assessed by broadband electric spectroscopy to shed light on the conduction mechanisms.The proposed conducting polymers combine the thermal stability of the aliphatic polyketone structure with the chemical flexibility given by the groups derived from functionalized amines branching out, proving to be highly tailorable, with possible applications in current energy conversion technologies. Acknowledgements: The authors wish to thank the Research Projects of Relevant National Interest (PRIN 2017) of the Italian Ministry of Education, University and Research “Novel Multilayered and Micro-Machined Electrode Nano-Architectures for Electrocatalytic Applications (Fuel Cells and Electrolyzers)” (Prot. 2017YH9MRK) and the SID2020 Project of the Department of Industrial Engineering, University of Padova “A New frontier in Hybrid Inorganic-Organic Membranes for Energy Conversion and Storage Devices” (Prot. BIRD201244) for funding.

Interplay between Conductivity, Matrix Relaxations and Composition of Ca‐Polyoxyethylene Polymer Electrolytes

AbstractIn this report, the conductivity mechanism of Ca2+‐ion in polyoxyethylene (POE) solid polymer electrolytes (SPEs) for calcium secondary batteries is investigated by broadband electrical spectroscopy studies. SPEs are obtained by dissolving into the POE hosting matrix three different calcium salts: CaTf2, Ca(TFSI)2 and CaI2. The investigation of the electric response of the synthetized SPEs reveals the presence in materials of two polarization phenomena and two dielectric relaxation events. It is demonstrated that the nature of the anion (i. e., steric hindrance, charge density and ability to act as coordination ligand) and the density of “dynamic crosslinks” of SPEs is fundamental in the establishment of ion‐ion/ion‐polymer interactions. The long‐range charge migration processes occurring along the two revealed percolation pathways of the electrolytes are generally coupled with the polymer host dynamics and depend on the temperature and the anion nature. This study offers the needed tools for understanding Ca2+ conduction in POE‐based electrolytes.

(Keynote) Hybrid Inorganic-Organic Ion-Exchange Membranes for Electrochemical Applications: Electrical Response and Conductivity Mechanism

Electrochemical energy conversion and storage (EECS) systems are of major interest for both industry and scientific community due to their high energy conversion efficiency and easy scalability [1]. Two families of EECS systems are attracting particular attention: ion-exchange membrane fuel cells and redox flow batteries (RFBs). On one hand, ion-exchange membrane fuel cells are particularly suited for light-duty vehicles and small-scale stationary systems (e.g., auxiliary power units) owing to their high energy and power densities. On the other hand, RFBs (with a particular reference to all-vanadium redox flow batteries, VRFBs) are ideally suited to the large-scale storage of energy for the power grid as they are characterized by a very high turnover efficiency and an outstanding cyclability.Electrolyte membranes (EMs) are found at the core of both ion-exchange membrane fuel cells and VRFBs. The role of such EMs is to: (i) keep separated the electroactive species involved in the redox reactions taking place at the electrodes and, at the same time, (ii) ensure a facile and selective migration of ions to prevent the polarization of the device and allow for the establishment of large current densities. As of today, the most widely adopted EMs for both ion-exchange membrane fuel cells and VRFBs are based on perfluorinated ionomers such as Nafion™ and other similar macromolecules [2]. These systems exhibit an outstanding proton conductivity and a very high chemical and electrochemical stability; however, they also suffer from important drawbacks such as: (i) a dramatic drop in conductivity at T > 80°C and in dry conditions; (ii) poor mechanical properties; and (iii) a large permeability to vanadium species [3, 4]. Consequently, it is often necessary to: (i) add humidification modules to ion-exchange membrane fuel cells, thus raising the bulk and cost of the device; or (ii) especially in the case of VRFBs, use thick EMs that curtail the current density.These drawbacks can be addressed by implementing several different strategies, that include: (i) the introduction of a filler in the EM, giving so rise to a hybrid inorganic-organic membrane [5]; (ii) the fabrication of the EM with a different macromolecule (e.g., a sulfonated polyaromatic system such as sulfonated polyether ether ketone, SPEEK [6]) and (iii) the doping of the EM with an ion-conducting medium (e.g., phosphoric acid [7], or a proton-conducting ionic liquid [8]). All of these strategies operate by modulating the physicochemical properties of the EMs, with a particular reference to the details of the phase segregation at the nano/mesoscale.This work overviews the study of the interplay between the physicochemical properties of hybrid ion-exchange membranes (with a particular reference to the chemical composition, thermoanalytical properties, morphology and structure), and the electrical response as determined by means of advanced investigation techniques such as Broadband Electrical Spectroscopy (BES). Results allow to: (i) elucidate the interactions between the different phases and components within each EM; and (ii) clarify the conductivity mechanism. On these bases, it is possible to identify the most promising avenues of research to devise EMs for application in ion-exchange membrane fuel cells and RFBs exhibiting a performance and a cyclability beyond the state of the art. Acknowledgement We acknowledge the support from: (a) the European Union’s Horizon 2020 research and innovation programme under grant agreement 881603; (b) the project “Advanced Low-Platinum hierarchical Electrocatalysts for low-T fuel cells” funded by EIT Raw Materials; and (c) the project “HELPER” funded by the University of Padova; and (d) the BIRD 2020 program of UNIPD.

(Invited) Innovative Olivine Cathodes for High-Voltage and High-Rate Lithium Batteries

Lithium batteries (LiBs) are among the most promising systems that could address today’s strongly increasing needs for an efficient, compact and reversible electrochemical storage of energy [1]. Indeed, LiBs are characterized by a high specific capacity, a high efficiency, and a long lifespan [2]. Unfortunately, improvements in the working potential, in the specific energy, and in the rate capability properties of the cathodes are still needed to comply with the specifications required by practical applications.This work describes the synthesis and the characterization of a new family of high-voltage and high-rate cathodes for LiBs. A high-performing olivine material of the type LiMPO4 (M = Fe, Ni, and Co) [3] has been modified by inserting into the structure high-valence transition metal ions (e.g., V(V), Nb(IV), and Ta(IV)) [4]. The effects of the insertion of the different ions on the structural, morphological, electrical and electrochemical properties of the materials have been thoroughly studied. The stoichiometry is evaluated by means of Inductively-Coupled Plasma Atomic Emission Spectroscopy (ICP-AES); the morphology and size distribution of the grains are characterized by Scanning Electron Microscopy (SEM) and High-Resolution Transmission Electron Microscopy (HR-TEM); the structure is examined by powder X-Ray Diffraction (XRD) as well as a variety of IR spectroscopy techniques. The electrochemical characterization is carried out by Cyclic Voltammetry (CV), Electrochemical Impedance Spectroscopy (EIS), and charge/discharge tests at different current rates. Finally, the conductivity mechanism is studied by Broadband Electrical Spectroscopy (BES). The cathode materials described in this report exhibit a high performance in terms of working potential (4.0 ÷ 5.0 V vs. Li/Li+), specific capacity (149 mAh∙g-1), and specific energy (656 mWh∙g-1). Moreover, the insertion of high-valence transition metals results in an improvement of the rate capability of the cathodes, allowing for fast charge and discharge processes.

A New Glass Forming Electrolyte Based on Lithium Glycerolate

The study of the interplay between structure and conductivity in lithium-conducting electrolytes is a pivotal point for the development of future secondary batteries [1]. The use of Glycerol as a low molecular weight component in electrolytes is particularly interesting due to its glass-forming behavior and low glass transition temperature (-78.5°C). In addition, a high flexibility of the alkyl backbone chain and the well-known capability of oxygen functionalities to coordinate lithium cations make Glycerol very appealing as ion-conducting media as well as building block to obtain hybrid polymer electrolytes [2].On this basis a family of eleven electrolytes based on Lithium Glycerolate with general formula C3H8-xO3Lix, where 0 ≤ x ≤ 1, is prepared and investigated [3]. In these electrolytes the Glycerolate (C3H8-xO3 x-) component acts as a large and flexible macro-anion which is able to provide a high single-ion conductivity to the material (8.36∙10-5 S∙cm-1 at 20°C and 1.55∙10-2 S∙cm-1 at 150°C for x = 0.25).Finally, the Glycerol∙∙∙Li+ interactions in these electrolytes are studied on T and x, with a particular reference to the detection of: a) macro-anion coordination sites; and b) the secondary structure of Glycerol chains. Insights on the long-range charge transfer mechanism and Glycerol relaxation events are also discussed.These studies are carried out by Inductively-Coupled Plasma Atomic Emission Spectroscopy, IR and Raman spectroscopies, DSC, TGA, and Broadband Electrical Spectroscopy.

Effect of plasticizer on the ion-conductive and dielectric behavior of poly(ethylene carbonate)-based Li electrolytes

Solid polymer electrolytes consisting of CO2-derived poly(ethylene carbonate) (PEC), LiPF6, and plasticizers (glycerol or 1-ethyl-3-methylimidazolium bis(trifluoromethane sulfonyl)imide, EMImTFSI) were prepared by a simple casting method, and their dielectric relaxation behavior was evaluated using broadband electric spectroscopy (BES), which clarified the correlation between the polymer motion and ionic conduction. From the DSC and BES results, it was revealed that the addition of plasticizer decreased the glass transition temperature and increased the dc conductivity (σdc) of the PEC electrolyte. The BES results also revealed that the plasticizer increased the segmental motion of PEC and improved σdc, and the plasticizing effect of EMImTFSI on the PEC electrolyte was larger than that of glycerol. From the results of the Walden plot and fragility analysis, it was expected that the degree of decoupling e and fragility m would increase with the addition of plasticizer because these plasticizers weaken the interactions between the PEC chains and Li ions in the electrolyte. Plasticized poly(ethylene carbonate) (PEC)/LiPF6 electrolytes were prepared and evaluated their ion-conductive and dielectric relaxation behavior using broadband electric spectroscopy (BES). The BES results indicated that the plasticizer accelerates segmental motion of PEC and improve the dc conductivity, and the plasticizing effect of ionic liquid (EMImTFSI) on the PEC electrolyte is larger than that of glycerol. From the results of the Walden plot and fragility analysis, it was revealed that the degree of decoupling and the value of fragility increase by the addition of plasticizer, and these plasticizers weaken interactions between PEC chains and Li ions in the electrolyte.

A New Glass Forming Electrolyte Based on Lithium Glycerolate

The study of the interplay between structure and conductivity in lithium-conducting electrolytes is a pivotal point for the development of future secondary batteries [1]. The use of Glycerol as a low molecular weight component in electrolytes is particularly interesting due to its glass-forming behavior and low glass transition temperature (-78.5°C). In addition, a high flexibility of the alkyl backbone chain and the well-known capability of oxygen functionalities to coordinate lithium cations make Glycerol very appealing as ion-conducting media as well as building block to obtain hybrid polymer electrolytes [2].On this basis a family of eleven electrolytes based on Lithium Glycerolate with general formula C3H8-xO3Lix, where 0 ≤ x ≤ 1, is prepared and investigated [3]. In these electrolytes the Glycerolate (C3H8-xO3 x-) component acts as a large and flexible macro-anion which is able to provide a high single-ion conductivity to the material (8.36∙10-5 S∙cm-1 at 20°C and 1.55∙10-2 S∙cm-1 at 150°C for x = 0.25).Finally, the Glycerol∙∙∙Li+ interactions in these electrolytes are studied on T and x, with a particular reference to the detection of: a) macro-anion coordination sites; and b) the secondary structure of Glycerol chains. Insights on the long-range charge transfer mechanism and Glycerol relaxation events are also discussed.These studies are carried out by Inductively-Coupled Plasma Atomic Emission Spectroscopy, IR and Raman spectroscopies, DSC, TGA, and Broadband Electrical Spectroscopy.

(Keynote) Electrical Response and Conductivity Mechanism in Ion-Exchange Membranes

Electrochemical energy conversion and storage systems are very important in today’s worldwide efforts to decarbonize the energy sector. Indeed, these systems exhibit a very high energy conversion efficiency, are easy to scale-up and are not affected by geographical constrains [1]. Two important examples of these systems are ion-exchange membrane fuel cells (IEMFCs) and redox flow batteries (RFBs). On one hand, ion-exchange membrane fuel cells are particularly suited for light-duty vehicles and small-scale stationary systems (e.g., auxiliary power units) owing to their high energy and power densities. On the other hand, redox flow batteries are ideally suited to the large-scale storage of energy for the power grid as they are characterized by a very high turnover efficiency and an outstanding cyclability [2].Electrolyte membranes (EMs) are present at the core of both IEMFCs and RFBs. The role of such EMs is to: (i) keep separated the electroactive species involved in the redox reactions taking place at the electrodes and, at the same time, (ii) ensure a facile and selective migration of ions to prevent the polarization of the device and allow for the establishment of large current densities. As of today, the most widely adopted EMs are based on perfluorinated ionomers such as Nafion™, SPEEK and other similar macromolecules [3, 4]. These systems exhibit a high conductivity, chemical and electrochemical stability; however, they also suffer from important drawbacks such as: (i) a dramatic drop in conductivity at T > 80°C and in dry conditions; (ii) poor mechanical properties; and (iii) a high permeability to active species (e.g., vanadium) [5]. Consequently, it is often necessary to: (i) add humidification modules to ion-exchange membrane fuel cells, thus raising the bulk and cost of the device; or (ii) especially in the case of vanadium redox flow batteries (VRFBs), use thick EMs that curtail the current density.These drawbacks can be addressed by implementing several different strategies, that include: (i) the introduction of a filler in the EM, giving rise to a hybrid inorganic-organic membrane [6]; (ii) the fabrication of EMs with different macromolecules (e.g., polybenzimidazole, PBI) [6-11]. All of these strategies operate by modulating the physicochemical properties of the EMs, with a particular reference to the phase segregation at the nano/mesoscale [3]. This work overviews the study of the interplay between the physicochemical properties (i.e., the chemical composition, thermoanalytical properties, morphology and structure) and the electrical response of hybrid ion-exchange membranes by means of advanced investigation techniques such as Broadband Electrical Spectroscopy (BES).The results allow to elucidate the interplay among chemical and physical properties of the different phases within each EM and their conductivity mechanism. Indeed, the understanding of the relationship taking place between structure and ion conduction mechanisms is crucial in order to trigger the development of new high-performing proton and anion conducting membranes for applications in fuel cells and redox flow batteries.