Development Of New Electrolytes Research Articles

(Keynote) Innovative Polymer Electrolytes for Secondary Lithium and Magnesium Batteries

The development of new electrolytes is a crucial target to devise secondary batteries running on alkaline- and alkaline-earth elements characterized by a high specific energy and power and an extensive cyclability, able to provide power for a wide range of applications ranging from portable electronic devices to electric vehicles. The electrolytes must satisfy very demanding requirements, including: (a) easy migration of the alkaline- and alkaline-earth cations between the electrodes of the battery; (b) high compatibility with all the other functional materials used in the assembly of the device; (c) wide potential window and excellent chemical stability. This report summarizes the preparation and characterization of innovative families of electrolytes meant to address these issues and opens the way for future research trends in this field. The investigated materials comprise: (i) single-ion-conducting nanocomposite polymer electrolytes; (ii) solid-state single-ion-conducting polymers; and (iii) conventional polymer electrolytes. In detail, the first approach comprises the study of nanocomposite polymer electrolytes (nCPEs) consisting of PEG400 and innovative lithiated fluorinated nanofillers (e.g., titanium or iron oxide) whose surface anion groups are neutralized with Li+ cations. These materials are single-ion conductors, and at room temperature they exhibit a Li+ conductivity higher than 10-5 S/cm. The second approach includes the investigation of Poly(vinyl alcohol)-based solid polymer electrolytes which are obtained by direct lithiation of partially hydrolyzed poly(vinyl alcohol), forming a lithium-poly(vinyl alkoxide) macromolecular salt. In this case it is possible to demonstrate a conductivity higher than 10-5 S/cm at RT upon plasticization with EMImTFSI ionic liquid. Finally, Broadband Electrical Spectroscopy (BES) studies of classic polymer electrolytes and innovative Magnesium salts for secondary Mg batteries will be presented. This technique will allow for the detailed elucidation of the interplay taking place between structure and conductivity of in these systems, thus tailoring the design of future polymer electrolytes. The chemical composition of the studied materials is analyzed by ICP-AES and microanalysis. The thermal properties are investigated by HR-TG and DSC measurements. The structure and the interactions in the materials are studied by vibrational spectroscopies (FT-MIR and –FIR). The electric response is elucidated by Broadband Electrical Spectroscopy (BES). Results allow to propose a conduction mechanism and to define the interplay existing between structural, thermal transitions and electrochemical properties of proposed innovative electrolytes. Acknowledgement This project has received funding from the BIRD 2016 program of UNIPD.

Advancements in Performance and Durability of Metal-Supported Solid Oxide Fuel Cells

Metal-supported solid oxide fuel cells (MS-SOFC) display a number of advantages over conventional all-ceramic SOFCs, including low-cost structural materials (e.g. stainless steel), mechanical ruggedness, excellent tolerance to redox cycling, and extremely fast start-up capability. These properties make MS-SOFCs ideally suited for range extenders in vehicles due to tolerance to thermal fluctuations following load changes or intermittent fuel flow. Directly fueled with ethanol or ethanol-water mixture, MS-SOFCs provide promising alternative for mobile applications. In this talk, the recent progress on performance and durability of symmetric MS-SOFCs, pioneered at LBNL, will be addressed. The development of new electrolyte, new cathode and anode catalysts, optimized cell configuration, and processing techniques will be discussed. The catalyst infiltration technique allows for flexible and layered electrode composition, depending on the system applications and fuels. Our current state-of-the-art MS-SOFCs achieve power density of ≥1.5 W/cm2 at 700 °C and ≥2.85 W/cm2 at 800 °C when fueled with humidified hydrogen which is, to the best of our knowledge, the highest performance reported in the literature for stainless steel MS-SOFCs. However, catalyst coarsening and Cr deposition from the stainless steel metal support are known to occur1, and the primary degradation mechanisms are elucidated and tackled to improve the durability. The cell area specific resistance (ASR) of <0.144 W∙cm2 at 700 °C meets the projected requirements for commercialization in vehicles. Initial studies on button cells fueled with ethanol/water mixture are investigated and further efforts towards increasing power density and durability are addressed. 1M.C. Tucker, Journal of Power Sources, 369, 6-12, Nov. 2017. Acknowledgments The information, data, or work presented herein was funded in part by the Advanced Research Projects Agency – Energy (ARPA-E), U.S. Department of Energy under work authorization number 13/CJ000/04/03. This work was funded in part by the U.S. Department of Energy under contract no. DE-AC02-05CH11231. Figure 1. (a) Illustration of a symmetric MS-SOFC configuration developed at LBNL, and (b) the highest cell performance obtained so far on the stainless steel MS-SOFCs. Figure 1

Blocking effect in promising proton conductors based on Ba3Ca1.18Nb1.82-xRxO9-δ (R = Y3+, Gd3+, Sm3+, Nd3+) ordered perovskites for PC-SOFCs

High proton conductivity and good chemical stability are keys to development of new electrolytes for PC-SOFCs as the next-future energy generation systems. However, the extensive use of new polycrystalline materials as solid electrolytes is still avoided, since the grain boundary response usually leads to a decrease in total conductivity due to electrical blocking effect. Here, we present our results on the space-charge modeling of impedance spectroscopy data obtained for Ba3Ca1.18Nb1.82-xRxO9-δ proton conducting ceramics, where x = 0, 0.30 and R = Y3+, Gd3+, Sm3+, Nd3+ are doping agents. Non-stoichiometric barium calcium niobate perovskites have received much attention as potential solid electrolytes for proton conducting solid oxide fuel cells. We show that despite their increased grain conductivity, the doped ceramics possess Schottky barriers that are higher than those observed for undoped Ba3Ca1.18Nb1.82O9-δ. In view of the space-charge model, proton depletion at the space-charge layer is the reason for the reduction of grain boundary conductivity in the doped compositions. Our findings are important for the understanding of proton conduction mechanisms in polycrystalline materials, which may allow future optimization of new doped electrolytes based on barium calcium niobate perovskites.

Development of Electrolytes for Single Crystal NMC532/Artificial Graphite Cells with Long Lifetime

NMC532/artificial graphite cells using single crystal NMC532 active material can have excellent long term lifetime at 4.4 V and elevated temperature if appropriate electrolytes are used. However, electrolytes developed earlier for these cells and reported in the literature cannot support even C/2 rates during charging without unwanted lithium plating at room temperature. This work is thus focused on the development of new electrolytes for single crystal NMC532/artificial graphite cells that can yield long lifetime and support higher charging rates. Ex-situ and in-situ gas measurements, ultra-high precision coulometry, isothermal microcalorimetry, lithium plating tests and long term cycling tests were used for the screening of electrolytes. Electrolytes with 2% vinylene carbonate (VC) + 1% ethylene sulfate (DTD) additives or 2% fluoroethylene carbonate (FEC) + 1% DTD additives yield single-crystal NMC532/graphite cells with long lifetime that can support C-rate charging at 20°C.

Effect of Solvents on the Behavior of Lithium and Superoxide Ions in Lithium-Oxygen Battery Electrolytes.

The molecular life of intermediates, namely, O2- and Li+ , produced during the discharge of aprotic Li-O2 batteries was investigated by molecular dynamics simulation. This work is of potential interest in the development of new electrolytes for Li-air batteries. We present the results on the structure and stability of the Li+ and O2- solvation shells and the thermodynamics and kinetics of the ion-association reaction in solvents such as dimethyl sulfoxide (DMSO), dimethoxyethane (DME), and acetonitrile (ACN). The residence time of solvent molecules in the Li+ solvation shell increases with the solvent donor number and is 100 times larger in DMSO than in ACN. In DMSO and DME, the Li+ ion diffuses with its solvation shell as a whole. On the contrary, in ACN it diffuses as a "bare" ion because of weak solvation. The rate constant for the association of the lithium ion with the superoxide anion in DMSO is two orders of magnitude slower than that in ACN due to fact that the free-energy barrier is 2.5 times larger in DMSO than in ACN. In addition, we show that despite the strong dependence of the Li+ shell stability on donor number, the rate of association does not necessarily correlate with this solvent property.

(Invited) Electrodeposition and Development of Mg and Ca Metal Anodes

Various metals have been used as battery anodes in electrochemical cells ever since the birth of batteries with Volta’s pile and also in the first commercialized primary (Zn/MnO2, Leclanché 1866) and secondary (Pb/acid, Planté 1859) batteries. The idea and prospects of building a technology based on lithium are much more recent, as it required moving away from aqueous electrolytes. However, the first Li-MoS2 cells with specific energy two or three times higher than the current Ni/Cd or Pb/acid cells were withdrawn from the market after safety difficulties were experienced with overheating on recharge related to dendrite growth. As an alternative, secondary Li-ion batteries avoiding the use of lithium metal anodes were commercialized by Sony in 1991. In contrast with Li metal anode, electrodeposition of Mg and Ca does not seem to be plagued with dendrite formation.1,2 In addition to the low cost of the raw materials ($5000/ton, $100/ton and $265/ton for Li2CO3, CaCO3 and MgO2, respectively), such alternative technologies would benefit from high standard reduction potentials (ca. -2.87 V and -2.37 V vs NHE for Ca and Mg, respectively, as compared to -3 V for Li) and high theoretical electrochemical capacities (both gravimetric and volumetric) for the metal electrode, while relying on the 5th (Ca) and 8th (Mg) most abundant elements on the Earth’s crust, respectively, whereas Li is the 25th. These metals are thus interesting candidates as anodes in rechargeable batteries. Pioneering research work by Aurbach et al.3,4 allowed to conclude that the electrochemical behavior of Ca and Mg metal anodes in conventional organic electrolytes is surface-film controlled, as is the case for Li, but Ca and Mg plating is virtually impossible, which was attributed to the lack of divalent cation transport through the passivation layer (solid electrolyte interphase or SEI). Therefore, research has been focusing on electrolyte formulation in which no SEI is formed. Recently Ca plating and stripping through a stable SEI layer has been demonstrated, setting out the basis for the development of new electrolytes for divalent cation based batteries with high resilience upon oxidation.2 The effect of several factors influencing the Ca deposition/stripping will be presented. Also, the reliability of the so called half-cell configuration in which Mg or Ca pseudo reference and counterelectrodes are used will be discussed and a systematic evaluation of the non-polarizability and stability in the electrolytic environment will be presented for these metal electrodes. Fig ure 1. Theoretical gravimetric and volumetric capacities for different anodes: metals and Li-ion.

List of Abstracts

. Production efficiency as well as the reduction of energy consumption and waste are the main drivers for the improvement of large-scale production in chemical industry. In addition, the demand for new processes – these days especially related to the chemical energy conversion as basis for the Energiewende – are additional triggers for innovation. Catalysis, well recognized by the public e.g. in form of the 3-way automobile catalyst, plays an important role for about 90% of all processes in chemical industry. The development of new and improved catalysts is a challenge for chemists – as is the search for new structural materials for mechanical engineers. Due to the often-necessary noble and thus expensive metals (e.g. palladium) in many catalysts, structural and chemical function have been developed separately in the two communities. Recent progress in catalytically active materials allows replacing expensive noble metals in selected catalytic processes by significant cheaper elements [1]. This offers the new perspective to combine structural and chemical functionality by innovative materials. Within this area, intermetallic compounds with their peculiar combination of crystal and electronic structure [2], represent an interesting class of materials to address this vision as will be shown in the contribution.

Development of New Electrolytes for Electropolishing of Niobium

1. Introduction In an international linear collider (ILC) plan, superconducting radio frequency (SRF) cavities are essential components for acceleration of the charged particles beam. The cavities are made of high purity niobium (Nb) and the inner surfaces of these cavities are required to be smooth enough because they play a crucial role in the performance of cavities. Typically, in order to obtain a good surface finish, electropolishing is used for the SRF cavities made of Nb. Typical electropolishing process uses the electrolyte composed of hydrofluoric acid (HF, about 55 mass%) and sulfuric acid (H2SO4, about 98 mass%) in a volumetric ratio of 1:91). However, there is a strong demand to replace the electrolyte with less hazardous one. In this study, we made a preliminary search for less hazardous electrolyte that could change the traditional HF-H2SO4 electropolishing system. 2. Experimental Following three types of electrolytes are tried for electropolishing of Nb: 3.7 M H2SO4, 10 M NaOH and 80 mass% CH3SO3H + 3 mass% NH4HF. A square of Nb (99% +, 20×20×0.5 mm3, Nilaco) is fixed on a Teflon holder (with exposed area of 1.13 cm2) and used as a working electrode. Before electropolishing, Nb samples is polished up to #6/0 SiC paper. A plate of aluminum is used as a counter electrode except in a NaOH solution where a nickel plate is used as a counter electrode. Electropolishing is carried out under constant voltage (5 – 10 V) for 30 min at temperatures of 30 - 80ºC. In each solution, I–V character and mass change are evaluated. The Nb surface after the electropolishing is characterized by a surface roughness meter and FE-SEM. 3. Experimental results and discussion In a 3.7 M H2SO4 solution at 30ºC, a blue oxide film was formed on Nb surface after applying 5 and 10 V. The results indicated that no polishing of Nb would proceed in this solution in a direct current mode. In a 10 M NaOH with constant voltages of 5 and 10 V, a gray-white oxide film was formed on Nb surface but no polishing proceeded either below 50ºC. At 80 ºC in a 10 M NaOH, a remarkable mass loss was observed at 10 V but the resultant surface was not very uniform. In a 80 mass% CH3SO3H + 3 mass% NH4HF at 30ºC, a gray-white oxide film formed on Nb surface at a constant voltage of 1 V. As the voltage is increased to 5 V, polishing proceeded most efficiently with mass loss of 4.3 mg cm-2 in 30 min. Further increase in voltage resulted in reduction in mass loss. The roughness of Nb surface was apparently improved in this solution. References 1) P. V. Tyagi, M. Nishiwaki, T. Noguchi, M. Sawabe, T. Saeki, H. Hayano, S. Kato, Applied Surface Sci., 285P, 778 (2013). 2) Japan patent JP2008-95192A Acknowledgment The authors are grateful to Tohoku Business Federation for their financial support.

Rational design of new electrolyte materials for electrochemical double layer capacitors

Abstract The development of new electrolytes is a centerpiece of many strategies to improve electrochemical double layer capacitor (EDLC) devices. We present here a computational screening-based rational design approach to find new electrolyte materials. As an example application, the known chemical space of almost 70 million compounds is investigated in search of electrochemically more stable solvents. Cyano esters are identified as especially promising new compound class. Theoretical predictions are validated with subsequent experimental studies on a selected case. These studies show that based on theoretical predictions only, a previously untested, but very well performing compound class was identified. We thus find that our rational design strategy is indeed able to successfully identify completely new materials with substantially improved properties.

Lithium-Sulfur Batteries: High Loading Cathode, New Electrolyte and Non-Lithium Metal Anode

Lithium sulfur battery (Li-S) has attracted intensive interest in recent years due to its high specific capacity, low cost, and abundant resources of sulfur. Theoretically, a high specific capacity of 1675 mAh g-1 and a specific energy of 2567 Wh kg-1 are expected for sulfur cathode. Practically, the energy density of Li-S battery is projected to be two to three times higher than that of state-of-the-art Li-ion batteries (180 Wh kg-1). However, the commercial applications of Li-S batteries are still hindered by several challenges.2 One is that with elevated sulfur loading above 3 mg/cm2, which is essential for high energy applications, new problems occur including the cathode cracking, electrode wetting and low sulfur utilization rate. The second and more detrimental issue that limits Li-S cell performance is interfacial stability and cycling reversibility of lithium metal anode, which easily reacts with both electrolyte solvents and the formed polysulfides during battery cycling and leads to unavoidable shuttle and continuous consumption of active sulfur species. These side reactions are significantly exacerbated under conditions of coupling with high-areal loading sulfur cathode and/or cycled at elevated current densities. As a result, thick and porous interface will be quickly built up on lithium anode and leads to quick impedance increase and thus fast capacity decay of the battery.3 The third problem is the amount of electrolyte required for full dissolution of the polysulfides. The dissolved polysulfides cause endless shuttle and continuous Li anode corrosion due to the lack of effective solid electrolyte interface (SEI) on lithium. In addition, the large amount of electrolyte significantly lowers the energy density of the battery, which is undesired for high-efficient portable devices or electric vehicle energy storage applications To overcome the aforementioned hurdles in Li-S batteries, multiple approaches have been proposed and successfully demonstrated by our group, spanning from sulfur cathode, anode and electrolyte. At the meeting, we will present our recent progresses on the Li-S battery system including the rational design of carbon/sulfur composite for large area and high loading sulfur cathode preparation, alternative non-Li anode materials for Li-ion sulfur batteries, and development of new electrolyte.

Electrolytes for high voltage electrochemical double layer capacitors: A perspective article

Abstract The development of innovative electrolyte components is nowadays considered one of the most important aspects for the realization of high energy electrochemical double capacitors (EDLCs). Consequently, in the last years many investigations have been dedicated towards new solvents, new salts and ionic liquids able to replace the current electrolytes. This perspective article aims to supply a critical analysis about the results obtained so far on the development of new electrolytes for high energy EDLCs and to outline the advantages as well as the limits related to the use of these innovative components. Furthermore, this article aims to give indications about the strategies could be used in the future for a further development of advanced electrolytes.

The amplifying effect of natural convection on power generation of thermogalvanic cells

Recent development of new electrolytes and electrode materials has shifted the research focus away from other routes to improved thermogalvanic cells, also known as thermocells or thermoelectrochemical cells. A thermogalvanic cell can be designed to achieve a relatively high maximum power output (Pmax) if convection is incorporated within the cell. Here we show through experimentation and modeling that natural convection is not a hindrance, but a plausible aid to improve power generation of thermogalvanic generators. The natural convection conditions are varied via orientation of the cell and electrode spacing. Experimental testing revealed an optimum concentration of 0.7M CuSO4 aqueous electrolyte, with the addition of 0.1M H2SO4 as background electrolyte, results in Pmax improvements of up to 100%, from ∼0.8 to ∼1.6μWcm−2, in a horizontal cell operating between the vertical cold and hot copper (Cu) electrode temperatures of 5 and 65°C, respectively. The experimental data reported here compare well with those from the few previously reported studies of Cu/Cu2+ cells. However, comparison with the conventional Fe(CN)64−/Fe(CN)63− cells revealed a completely different dependence of the electrode spacing on the power generation, that the Pmax of Cu/Cu2+ cell increases, instead of decreases, with the electrode spacing due to the difference in ionic transfer mechanism. Herein, we also develop a simple expression which predicts the ratio between the Pmax of a thermogalvanic generator with and without convection in terms of Sherwood, Nusselt, and Lewis numbers. The predictions are in reasonable agreement with our experimental data; both show that convection is primarily responsible for the enhancement in Pmax of thermogalvanic generators.

Invited Presentation: Addressing Capacity Fading Challenges in Li-S Batteries via Electrolyte/Cathode Design

The presentation will focus on recent work in our lab involving the development of new electrolytes for the Li-S cell along with new materials for the cathode and developing insightful in situ probes of redox processes for a working cell and understanding the cathode interface. We consider these to be the most challenging issues in electrochemical energy storage cells that operate on the basis of chemical transformations, where the factors that govern capacity and cycling stability are difficult to access owing to the amorphous nature of the intermediate species. I will present results on cathodes for the Li-S cell comprised of sulfur-imbibed robust spherical carbon shells with tailored porosity that exhibit excellent cycling stability. Their highly regular nanoscale dimensions and thin carbon shells allow highly uniform electrochemical response and enable direct monitoring of sulfur speciation within the cell over the whole redox range by operando X-ray absorption spectroscopy on the S K-edge. These studies are coupled with solid state NMR investigations, and include investigations of novel electrolyte systems. Functional tailoring of the surface of the shells will also be presented, and if time permits, comparison will be drawn with Li-O2 electrochemistry.

Nonflammable perfluoropolyether-based electrolytes for lithium batteries

The flammability of conventional alkyl carbonate electrolytes hinders the integration of large-scale lithium-ion batteries in transportation and grid storage applications. In this study, we have prepared a unique nonflammable electrolyte composed of low molecular weight perfluoropolyethers and bis(trifluoromethane)sulfonimide lithium salt. These electrolytes exhibit thermal stability beyond 200 °C and a remarkably high transference number of at least 0.91 (more than double that of conventional electrolytes). Li/LiNi1/3Co1/3Mn1/3O2 cells made with this electrolyte show good performance in galvanostatic cycling, confirming their potential as rechargeable lithium batteries with enhanced safety and longevity.

3D Anhydrous Proton-Transporting Nanochannels Formed by Self-Assembly of Liquid Crystals Composed of a Sulfobetaine and a Sulfonic Acid

Herein we describe anhydrous proton transportation through 3D interconnected pathways formed by self-assembled molecular complexes. A thermotropic bicontinuous cubic (Cub(bi)) phase has been successfully obtained by mixing a wedge-shaped sulfobetaine with benzenesulfonic acid in different ratios. These ionic complexes exhibit the Cub(bi) phase in a wide range of temperatures, while the single zwitterionic compound shows only a columnar hexagonal phase, and benzenesulfonic acid is nonmesomorphic. Anhydrous proton conduction on the order of 10(-4) S cm(-1) has been achieved for the mixture in the Cub(bi) phase over 100 °C, which can be useful for the development of new electrolytes for the next generation of fuel cells.

Mobile charge carrier concentration and mobility of a polymer electrolyte containing PEO and Pr 4N + I − using electrical and dielectric measurements

For the characterization and development of new electrolytes it is important to know the number of free charge carriers and their mobility. A new method has been developed to estimate the charge carrier density, n, and mobility, μ, for an electrolyte using dielectric measurements and a space charge relaxation model. In order to verify the applicability of this method, it has been tested with an aqueous KI solution electrolyte. The method was then applied to a polyethylene oxide (PEO) based polymer electrolyte. In the case of the polymer electrolyte, plasticized and non plasticized electrolytes intended for photo-electrochemical solar cells containing Pr 4N + I − salt which is an iodide ion conductor at room temperature was used. The significant conductivity increase that occurs during the PEO crystallite melting is shown to be due to a large and abrupt increase of the concentration of mobile charge carriers. It is also shown that, for the PEO above the crystallite melting temperature, the introduction of the plasticizer results in an increased mobility. Results from the solution electrolyte show good agreement with known values.

Tape casting of new electrolyte and anode materials for SOFCs operated at intermediate temperature

An important task in SOFC research is the reduction of the operating temperature to 700 °C, to avoid premature ageing of the cell components and the use of expensive interconnect materials. This requires the development of new electrolytes and electrodes materials. Oxyapatite electrolytes have recently attracted considerable attention and we have already reported some interesting performances for the La 9Sr 1Si 6O 26.5 composition ( σ = 8.8 × 10 −3 S cm −1 at 700 °C) [Beaudet Savignat, S., Lima, A., Barthet, C. and Henry, A., In Proceedings of the International Symposium Solide Oxide Fuel Cells VIII, Vol. 2003–2007, pp. 372–378]. This study was centered on the manufacturing of an apatite electrolyte and a Ni/apatite cermet anode by the tape casting process, with a view to the development of anode/electrolyte 1/2 cells. Slurries compositions were first optimized to adjust green tapes characteristics. Secondly, we focused on the binder burnout and the sintering. Dense electrolytes were synthesized. The influence of the particle size of the apatite powder, with a fixed NiO powder particle size, and the influence of the addition of pyrolyzable organic particles on the sintering and the microstructure of the anode material were studied.

Elaboration and Ionic Conduction of Apatite-Type Rare Earth Oxides

We synthesized lanthanoid silicates and germanates with the apatite structure such as La 10-x AE x Si 6 O 27-x/2 with AE = Ca and Sr, La 10-x Y x Si 6 O 27 and La 10-x Ge 6 O 27-3x/2 , with a view to the development of new electrolytes having good oxide-ion conductivities under 800°C for intermediate operating temperature solid oxide fuel cells (SOFCs). These ceramics were prepared by the mixed oxide route. Densities above 95% of the theoretical density were obtained. X-ray diffraction spectra evidenced a hexagonal apatite structure as a major phase. Conductivities as high as 1.4 10 -2 S.cm -1 were measured at 700°C.

Bismuth oxide-based solid electrolytes for fuel cells

During the last three decades, a large number of investigations has been reported pertaining to the science and technology of solid oxide fuel cells (SOFCs) based mainly on the yttria-stabilized zirconia (YSZ) electrolyte. Because of the problems associated with the high temperature of operation (~ 1000°C) of the YSZ-based cells, there has been a substantial effort to develop alternative electrolytes with ionic conductivity comparable to that of YSZ at relatively lower temperatures. This review presents a systematic evolution in the area of the development of new electrolytes based on bismuth sesquioxide for fuel cell applications at moderate temperatures.