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For the energy transition to succeed, the growing amount of solar and wind power need to be stored for night-time or low-wind periods. Redox flow storage offers a good way of balancing out the fluctuations in renewable energies and is considered a promising energy storage system because it is potentially inexpensive and relatively easy to scale. However, the costs are still too high for this technology to be a resounding success. New manufacturing and joining technologies can help here. This will be demonstrated using the central element of the redox flow battery, the stack, as an example. Here, novel bonding ideas will be investigated and explained. The aim was to improve the contact between the gas diffusion fleece on the active side of the bipolar half plates and the current collector on the bipolar edge plates. A media and temperature-resistant adhesive was tested and tried out in different geometries.

Recently, zinc-air batteries have received revived interest as one of the proposed post lithium-ion technologies. This revival is driven by the demand for safe and environmentally friendly energy storage solutions for fluctuating renewable energy. These energy storage systems need to address variable power, capacity and profitability requests. Zinc-air-flow batteries with high specific energy density, low-cost, highly available and eco-friendly active materials are suitable to fulfill these requirements. The use of a flow battery type with zinc-particles suspended in an alkaline solution (zinc-slurry) in addition to high performance oxygen-reduction electrodes enables the development of high-power zinc-air batteries. Usually, the energy density of zinc-air-flow cells is limited by the solubility of the oxidation products in the electrolyte. In our cell, the electrolyte is supersaturated with oxidation products, before finally ZnO precipitates from the electrolyte. The cell is therefore operated beyond zincate solubility limit, which allows higher specific capacities than reported in literature, even though the zincate solubility of the electrolyte is much lower than reported [1]. The flow cell has an active area of 100 cm² and incorporates a copper plate as current collector for the zinc-suspension electrode and an oxygen reduction electrode with gas-diffusion layer (supplied by Covestro). The zinc-slurry contains zinc-particles (supplied by Grillo) suspended in an alkaline solution (30 wt.-% KOH) and stabilized with polyacrylic acid. One of the main limiting factors of the specific capacity of the zinc-slurry is passivation. While the passivation of stationary electrodes in flowing or quiescent electrolytes is fairly well understood, see e. g. [2], there is no literature on the passivation behaviour of zinc-slurry electrodes. In this study we determined the starting point of ZnO precipitation and the critical factor for the passivation of these anodes by analysing cell voltage, potential of the zinc electrode and the zincate concentration in the liquid phase of the zinc-slurry. Depending on parameters like current density and additive selection, it is possible to reach specific capacities of 287 mAh/gslurry or 574 mAh/gzinc. Appleby, A.J. and M. Jacquier, The C.G.E. circulating zinc/air battery: A practical vehicle power source. Journal of Power Sources, 1976. 1(1): p. 17-34. Bockelmann, M., et al., Electrochemical characterization and mathematical modeling of zinc passivation in alkaline solutions: A review. Electrochimica Acta, 2017. 237: p. 276-298.

The mechanical recharge of zinc-air batteries is described in this chapter. These systems can be divided into mechanically rechargeable systems with cassettes and hydraulically rechargeable systems with either pumped electrolyte or pumped zinc slurry. A zinc slurry usually consists of zinc particles in a binder-stabilized alkaline electrolyte. A special feature of the hydraulic systems is that the power (size of the active electrode area) and the capacity of the battery (size of the electrolyte tank) can be scaled independently of each other. Hydraulically rechargeable zinc-air technologies can either be operated below or above the zincate solubility limit. These two operation modes show significant differences with respect to the maximum achievable specific capacity and specific energy of the battery system. Further characteristics of zinc slurry electrodes are described with focus on the energy density and the electrolyte conductivity. The chapter also contains a description of discharge characteristics which includes power densities and depth-of-discharge with passivation effects, as well as methods to determine the state of charge. In addition, an overview on the development history of mechanically rechargeable zinc-air batteries is given. This includes among others the work at Compagnie Generale d'Electricite (CGE) and Pinnacle Research Institute with slurry-based systems. The work with pumped electrolyte systems with a static bed of zinc articles at Lawrence Livermore National Laboratory and Metallic Power/Zincnyx/MGX Renewables are also described. Additionally the work with mechanically rechargeable cassettes at Electric Fuel Limited is reported. The chapter concludes with an assessment of the operational capability of mechanically and hydraulically rechargeable zinc-air batteries and a comparison with other metal-air batteries.

The aim of this research is an evaluation of polyelectrolytes. In the application of zinc-iodine batteries (ZIBs), polyelectrolytes have high stability, good cationic exchange properties and high ionic conductivity. Polyelectrolytes are also cost-effective. Important component of ZIBs are cation exchange membranes (CEMs). CEMs prevent the crossover of iodine and polyiodide from zinc (Zn) electrodes. However, available CEMs are costly and have limited ionic conductivity at room temperature. CEMs are low-cost, have high stability and good cationic exchange properties. Herein, polyelectrolyte membranes prepared from carboxymethyl cellulose (CMC) and polyvinyl alcohol (PVA) are examined. It is seen that an increase in the ratio of PVA leads to enhanced ionic conductivity as well as increased iodine and polyiodide crossover. ZIBs using polyelectrolytes having 75:25 wt.% CMC/PVA and 50:50 wt.% CMC/PVA show decent performance and cycling stability. Due to their low-cost and other salient features, CMC/PVA polyelectrolytes prove they have the capacity for use as cation exchange separators in ZIBs., Chemical Engineering; Energy; Materials Science; Chemical Energy Storage; Electrochemical Energy Engineering; Energy Storage Technology; Polymers; Electrochemistry; zinc-iodine battery; polyiodide crossover; ionic conductivity; cationic exchange; anionic polyelectrolyte.

A novel nanocomposite consisting of gas-phased produced Si nanoparticles, carbon nanotubes (CNTs), and polyaniline (PANi) is developed as an anode material (Si-CNT/PANi) for lithium-ion batteries. This nanocomposite integrates the merits from its three components, where Si nanoparticles provide high capacity, CNTs act as an electrically conductive and mechanically flexible network, and PANi coating further enhances the electrical conductivity and protects the silicon structure. An anode made of this nanocomposite shows a high reversible capacity of 2430 mAh/g with good capacity retention over 500 cycles compared to pristine Si. The Si-CNT/PANi nanocomposite also demonstrated a high Coulombic efficiency and improved rate-capabilities.

Silicon is a potential anode material for lithium-sulfur batteries. This future energy storage system has an essential higher energy density and significantly lower costs compared to lithium-ion batteries. However, a big problem by using silicon is the high volume expansion of 280 %. The volume expansion and contraction results in a break-up of the solid electrolyte interface (SEI). The SEI has to be reformed continuously during cycling, which leads to a continuous loss of lithium. One approach to compensate the lithium loss during cycling is the prelithiation of silicon anode with a stabilized lithium metal powder (SLMP ® ). SLMP can serve as an additional lithium source to mitigate the capacity loss during the first and the following cycles and improve the energy density significantly. Adding SLMP directly into the slurry during electrode production is problematic because it is incompatible with many conventional electrode components. Therefore the application of SLMP on the finished electrode as an additional layer is advantageous. For this purpose, the SLMP can be mixed in a solvent and applied to the electrode. After drying, the SLMP must still be activated by a pressing process, since the protective carbonate shell must be broken open. One problem here is the rapid separation of SLMP and solvent. A possible solution is the addition of a binder, like styrene-butadiene rubber (SBR). Here we present a silicon/graphene-based anode prelithiated with SLMP in the electrolyte systems 1 M LiTFSI, 0.2 M LiNO3 in dimethoxy ethane (DME) and 1,3-dioxolane (DOL). For this work, we used a commercially available Si/C composite material with a PAA binder. The silicon content of the electrode is 25 %. SLMP is loaded on the top of the electrode and activated by a pressing process. The advantage of a binder in the SLMP - solvent mixture will be shown, and also that the binder has no negative effect on the electrochemical properties. The electrodes are examined by galvanostatic cycling and show high coulomb efficiency of over 85 % in the first cycle. Also, the SLMP of the anode compensates the lithium loss over at least 300 cycles. We will show the improvements of the anode prelithiated with SLMP compared to pure Si/C anodes.

As one of the proposed post lithium-ion technologies, zinc-air batteries have received revived interest in the recent years, which is driven by the increased demand of high-performance, efficient, safe and environment-friendly energy storage solutions. These energy storage systems need to address variable power, capacity and profitability requests. Zinc-air flow batteries with higher specific energy density than lithium-ion and low-cost, highly available, eco-friendly active materials are suitable to fulfill these requirements. The energy density of most zinc-air flow batteries is limited by the low solubility of ZnO in the electrolyte. The use of a flow battery type with zinc-particles suspended in alkaline solution (zinc-slurry) in addition with high performance oxygen-reduction electrodes enables the development of high-power zinc-air batteries. This setup also enables the independent scaling of capacity and power. The cooperative project, ZnMobil, funded by the Federal Ministry of Economic Affairs and Energy in Germany, combines the experience of industrial and academic partners (Covestro Deutschland AG; Grillo-Werke AG; VARTA Microbattery GmbH; Accurec Recycling GmbH; Technical University Freiberg, Gottfried Wilhelm Leibniz University Hannover; University of Duisburg-Essen; the fuel cell research center ZBT GmbH) to develop a high-performance and low-cost zinc-air flow battery. The battery system consists of a 100 cm² copper plate as current collector for the zinc-suspension electrode and an oxygen reduction electrode with gas-diffusion layer (supplied by Covestro Deutschland AG). The zinc-slurry contains zinc particles (supplied by Grillo-Werke AG) suspended in alkaline solution (30 wt-% KOH) and stabilized with polyacrylic acid. Here we present a systematic study regarding the effects of the discharge products on the cell performance. Depending on the state of discharge and operation parameters the discharge product ZnO causes several important effects. The solid ZnO limits the discharge capacity in several ways. At high current densities, passivation is the main topic. If passivation is avoided, e.g. with the help of additives, the solid ZnO causes a viscosity increase until the cell is blocked. For this study we evaluated parameters like cell voltage, cell resistance, slurry viscosity, ZnO concentration in the electrolyte and other parameters in correspondence to the state of discharge. The understanding of these effects is essential to build a hydraulically rechargeable battery with high zinc usage and therefore high energy densities. Depending on parameters like current density and additive selection, it is possible to reach more than 70 % DOD, which corresponds to 287 mAh/gslurry or 574 mAh/gzinc. A demonstrator-cell was operated for more than 140 h. During this time it was successfully hydraulically recharged several times.

In this study, we present a novel anode architecture for high-performance lithium-ion batteries based on a Silicon/3-aminosilane-functionalized CNT/Carbon (Si/A-CNT/C) composite. A high-yield, low-cost approach has been developed to stabilize and support silicon as an active anode material. Silicon (Si) nanoparticles synthesized in a hot-wall reactor and aminosilane-functionalized carbon nanotubes (A-CNT) were dispersed in styrene and divinylbenzene (DVB) and subsequently polymerized forming a porous Si/A-CNT/C composite. Transmission electron microscopy showed that this method enables the interconnection and a uniform encapsulation of Si nanoparticles within a porous carbon matrix especially using aminosilane-functionalized CNT (A-CNT). Electrochemical characterization shows that this material can deliver a delithiation capacity of 2293 mAh g−1 with a capacity retention of more than 90 % after 200 cycles at lithiation and delithiation rate of 0.5 C. We conclude that the porous Si/A-CNT/C composite material can accommodate sufficient space for Si volume expansion and extraction and improve the electronic and ionic conduction. Excellent electrochemical performance during repeated cycling can thus be achieved.

The increased use of fluctuating renewable energy calls for efficient, safe and environmentally friendly energy storage solutions. To meet the variable power-, capacity- and profitability requests of mobile and stationary applications, it is necessary to identify promising materials. Zinc-air batteries with specific energy density higher than lithium-ion and low cost, highly available, eco-friendly active materials are suitable to fulfill these requirements. The use of a flow battery type with zinc-particles suspended in alkaline solution (zinc-slurry) in addition with high performance oxygen-reduction electrodes enables the development of high-power zinc-air batteries. This setup also allows the independent scaling of capacity and power. The recharging of this system can be performed due to classical electrical charging or due to a hydraulic recharge by changing the used zinc-slurry with a fresh one. The cooperative project, ZnMobil, funded by the Federal Ministry of Economic Affairs and Energy in Germany combines the experience of industrial and academic partners (Covestro Deutschland AG; Grillo-Werke AG; VARTA Microbattery GmbH; Accurec Recycling GmbH; Technical University Freiberg, Gottfried Wilhelm Leibniz University Hannover; University of Duisburg-Essen; the fuel cell research center ZBT GmbH) to develop a zinc-air flow battery with high performance and economic efficiency. Here we present strategies for the hydraulic recharging of zinc-air flow batteries. The battery system consists of a 100 cm² copper plate as current collector for the zinc-suspension electrode and an oxygen reduction electrode with a gas-diffusion layer (supplied by Covestro Deutschland AG). The zinc-slurry contains zinc particles (supplied by Grillo-Werke AG) suspended in alkaline solution (30 wt.-% KOH) and stabilized with polyacrylic acid. Depth-of-discharge and battery resistance were measured for zinc-slurries in a flow system under regulated conditions. The influence of the depth-of-discharge and several additives on the rheology of the zinc-slurries was evaluated. Depending on the current density and additive selection, it is possible to achieve energies of up to 300 Wh during discharge.

The current energy system is subject to a fundamental transformation: A system that is oriented towards a constant energy supply by means of fossil fuels is now expected to integrate increasing amounts of renewable energy to achieve overall a more sustainable energy supply. The challenges arising from this paradigm shift are currently most obvious in the area of electric power supply. However, it affects all areas of the energy system, albeit with different results. Within the energy system, various independent grids fulfill the function of transporting and spatially distributing energy or energy carriers, and the demand-oriented supply ensures that energy demands are met at all times. However, renewable energy sources generally supply their energy independently from any specific energy demand. Their contribution to the overall energy system is expected to increase significantly. Energy storage technologies are one option for temporal matching of energy supply and demand. Energy storage systems have the ability to take up a certain amount of energy, store it in a storage medium for a suitable period of time, and release it in a controlled manner after a certain time delay. Energy storage systems can also be constructed as process chains by combining unit operations, each of which cover different aspects of these functions. Large-scale mechanical storage of electric power is currently almost exclusively achieved by pumped-storage hydroelectric power stations. These systems may be supplemented in the future by compressed-air energy storage and possibly air separation plants. In the area of electrochemical storage, various technologies are currently in various stages of research, development, and demonstration of their suitability for large-scale electrical energy storage. Thermal energy storage technologies are based on the storage of sensible heat, exploitation of phase transitions, adsorption/desorption processes, and chemical reactions. The latter offer the possibility of permanent and loss-free storage of heat. The storage of energy in chemical bonds involves compounds that can act as energy carriers or as chemical feedstocks. Thus, they are in direct economic competition with established (fossil fuel) supply routes. The key technology here – now and for the foreseeable future – is the electrolysis of water to produce hydrogen and oxygen. Hydrogen can be transformed by various processes into other energy carriers, which can be exploited in different sectors of the energy system and/or as raw materials for energy-intensive industrial processes. Some functions of energy storage systems can be taken over by industrial processes. Within the overall energy system, chemical energy storage technologies open up opportunities to link and interweave the various energy streams and sectors. Chemical energy storage not only offers means for greater integration of renewable energy outside the electric power sector, it also creates new opportunities for increased flexibility, novel synergies, and additional optimization. Several examples of specific energy utilization are discussed and evaluated with respect to energy storage applications. The article describes various technologies for energy storage and their potential applications in the context of Germany’s Energiewende, i.e. the transition towards a more sustainable energy system. Therefore, the existing legal framework defines some of the discussions and findings within the article, specifically the compensation for renewable electricity providers defined by the German Renewable Energy Sources Act, which is under constant reformation. While the article is written from a German perspective, the authors hope this article will be of general interest for anyone working in the areas of energy systems or energy technology.

In the recent years, rechargeable lithium-ion batteries have gained in importance for electronic devices and electric vehicles. Thus, research and development focuses on improving energy and power densities as well as durability of lithium-ion batteries. Especially for high energy and power densities, the electrode materials must possess high specific storage capacities and coulometric efficiencies. However, state-of-the-art anode and cathode electrode materials, e.g. graphite and LiFePO4 exhibit high coulometric efficiencies but rather low theoretical storage capacities (372 and 170 mAh/g, respectively). In the last decade silicon has become a promising anode material due to its high theoretical specific capacity of 3579 mAh/g at ambient temperature. However, this high specific storage capacity owing to host up to 3.75 lithium atoms per silicon atom leads to extreme volume expansion up to 280 % during lithiation, which results in pulverization and delamination of the electrode material after few cycles. Various approaches have been conducted to overcome these issues e.g. by using nano-sized active material or carbon coated silicon composite material. In addition to the materials science the electrode structure is of particular importance for the electrochemical performance. Electrode composition, binding mechanism due to the use of suitable binder polymers or particle size distribution of the active material are some exemplary parameters to stabilize the electrode structure and to handle such high mechanical stress during lithiation/delithiation. Here we present electrochemical investigations of high capacity and high efficiency graphene coated silicon nanocomposite based electrodes prepared by using a wet chemical doctor blade manufacturing process. This active material provides a capacity of >2000 mAh/g with efficiencies >99% over more than 500 cycles. Investigations focus on influence of the stability of the electrode structure by using impedance spectroscopy, scanning electron microscopy, confocal microscopy and estimation of the coating adhesion strength. Cyclic voltammetry and galvanostatic cycling will show the applicability of improved Si/C composite based electrodes compared to conventional graphite based electrodes for lithium-ion batteries both in half cells as well as full cells in combination with commercially available cathode material.

A robust and electrochemically stable 3D nanoheterostructure consisting of Si nanoparticles (NPs), carbon nanotubes (CNTs) and reduced graphene oxide (rGO) is developed as an anode material (Si–CNT/rGO) for lithium-ion batteries (LIBs). It integrates the benefits from its three building blocks of Si NPs, CNTs, and rGO; Si NPs offer high capacity, CNTs act as a mechanical, electrically conductive support to connect Si NPs, and highly electrically conductive and flexible rGO provides a robust matrix with enough void space to accommodate the volume changes of Si NPs upon lithiation/delithiation and to simultaneously assure good electric contact. The composite material shows a high reversible capacity of 1665 mAh g−1 with good capacity retention of 88.6 % over 500 cycles when cycled at 0.5 C, that is, a 0.02 % capacity decay per cycle. The high-power capability is demonstrated at 10 C (16.2 A g−1) where 755 mAh g−1 are delivered, thus indicating promising characteristics of this material for high-performance LIBs.

Das Energiesystem steht vor einem grundlegenden Wandel: Ein System, das auf die konstante Bereitstellung durch fossile Energieträger ausgerichtet ist, soll durch die umfangreiche Integration erneuerbarer Energien eine nachhaltigere Energieversorgung gewährleisten. Die Herausforderung des Systemwechsels macht sich gegenwärtig in der Stromversorgung am deutlichsten bemerkbar, betrifft aber alle Bereiche des Energiesystems, wenn auch mit unterschiedlichen Auswirkungen. Im Energiesystem werden Energie und/oder Energieträger räumlich von Energieversorgungsnetzen verteilt, während die bedarfsgerechte Bereitstellung gegenwärtig dafür sorgt, dass der Energiebedarf zu jeder Zeit gedeckt wird. Energie aus erneuerbaren Quellen wird in der Regel nicht bedarfsgerecht bereitgestellt; ihr Anteil steigt. Energiespeicher sind eine Möglichkeit, das zeitlich versetzte Angebot mit der Nachfrage zur Deckung zu bringen. Energiespeicher sind Systeme, die eine Energiemenge kontrolliert aufnehmen, sie über einen im Kontext relevanten Zeitraum in einem Speichermedium zurückhalten und mit zeitlicher Verzögerung wieder kontrolliert abgeben können. Zu den Energiespeichern gehören nach dieser Definition auch Verfahrensketten, die diese Aspekte durch eine Kombination verschiedener Technologien abbilden. Als mechanische Großspeicher für elektrischen Strom dienen heute fast ausschließlich Pumpwasserspeicherkraftwerke, die zukünftig durch Druckluftspeicherkraftwerke und eventuell Luftzerlegungsanlagen ergänzt werden könnten. Im Bereich der elektrochemischen Energiespeicher befinden sich verschiedene Technologien im Forschungs-, Entwicklungs- und/oder Demonstrationsstadium für einen Einsatz in der stationären großtechnischen Stromspeicherung. Thermische Speichertechnologien beruhen auf der Speicherung von sensibler Wärme, der Ausnutzung von Phasenübergängen, Adsorption-/Desorptionsprozessen oder chemischen Reaktionen, die prinzipiell eine dauerhafte und verlustfreie Speicherung von Wärme ermöglichen können. Die Speicherung von Energie in Form chemischer Bindungen in stofflichen Speichern verläuft über Substanzen, die selbst als Energieträger oder Chemikalien verwendet werden können; sie befinden sich damit in direkter Konkurrenz zu alternativen Bereitstellungs- und Nutzungsvarianten. Die Schlüsseltechnologie hierbei ist auf absehbare Zeit die Elektrolyse von Wasser zu Wasserstoff und Sauerstoff. Wasserstoff kann wiederum durch verschiedene Verfahren in andere Energieträger umgewandelt werden. So lässt er sich in verschiedenen Sektoren des Energiesystems und/oder in energieintensiven Industrieprozessen stofflich nutzen. Teilfunktionen von Energiespeichern können auch von Industrieprozessen wahrgenommen werden. Dem Energiesystem in seiner Gesamtheit eröffnen sich neue Optionen, die bisher weitgehend getrennten Energieversorgungsströme zu verknüpfen und zu vernetzen. Neben der Möglichkeit, verstärkt erneuerbare Energien außerhalb des Stromsektors zu nutzen, ergeben sich auch neue Bedingungen für eine verstärkte Flexibilisierung, neuartige Synergieeffekte und zusätzliche Optimierungsmöglichkeiten. Anhand verschiedener Referenzfälle wird der mögliche Einsatz von Speichertechnologien aufgezeigt und bewertet. OA hybrid

In the recent years, rechargeable lithium-ion batteries (LIBs) have gained in importance for electronic devices and electric vehicles. Thus, research and development focuses on improving energy and power densities as well as durability of LIBs. Currently, commercially available graphite anodes with a specific capacity of 372 mAh g–1 are used, but these cannot satisfy the abovementioned demands. Silicon is a very promising candidate as an anode material due to its high theoretical capacity of 3579 mAh g–1 at room temperature (according to the formation of the Li15Si4alloy). However, this high specific capacity owing to host up to 3.75 lithium atoms per silicon atom leads to extreme volume expansion up to 300% during lithiation, which results in pulverization and delamination of the electrode material after few cycles. Various approaches have been conducted to overcome these issues e.g. by using nanosized active material or carbon-based silicon composites. Nanosized structures can shorten the diffusion pathways of the lithium-ions, thus facilitating rapid lithiation and delithiation processes. In addition, smaller sized structures can also significantly reduce the inner-mechanical stress of the materials during lithiation/delithiation of the active material. Carbon-based additives, e.g. carbon nanotubes (CNTs) for forming nanocomposites with silicon nanostructures can not only improve the electrical conductivity of the silicon anodes, but can also effectively accommodate the large volume changes of silicon nanoparticles (Si NPs) during the electrochemical reactions. ln this study, we propose a new strategy using reduced graphene oxide (rGO) in combination with a stabilized Si-CNT hybrid to generate a robust, highly conducting nanoheterostructure to further enhance the stability and the electrochemical performance of silicon-based electrode materials. Si NPs were synthesized in the gas phase by decomposition of monosilane in a hot-wall reactor. Si NPs and CNTs were functionalized and reacted to form the Si-CNT hybrids, utilizing the formation of peptide bonds between amine-modified Si NPs and the carboxyl-functionalized CNTs. This chemical linking is the first step to improve the binding strength between the Si NPs and an electrically conducting network. The Si-CNT hybrid was combined with GO to self-assemble to form a robust nanoheterostructure, which is subsequently reduced. Si NPs, CNTs, and rGO sheets play important roles in this unique nanoheterostructure as LIB anode. Si NPs provide high capacity, rGO ensures high electrical conductivity for the entire structure and provides sufficient void spaces to buffer the volume changes of the Si NPs, and CNTs act as the scaffolding to bind the Si NPs and provide additional electrically-conductive channels. Here we present electrochemical investigations of silicon anodes based on Si-CNT/rGO nanoheterostructure nanocomposite material. The electrode preparation is based on a well-established wet chemical doctor blade manufacturing process using a water based binder. The nanocomposite material shows a high reversible capacity of 1665 mAh g–1 with good capacity retention of 88.6% over 500 cycles when cycled at 0.5 C, that is, a 0.02% capacity decay per cycle. The high-power capability is demonstrated at 10C (16.2 Ag-1) where 755 mAh g–1 are delivered. Full cell experiments demonstrate the applicability of improved silicon anodes for lithium-ion batteries.

In recent years, zinc-air flow batteries have regained importance as promising energy storage system for mobile and stationary applications. This revived importance is driven by the increased demand of high-performance, efficient, safe and environmentally friendly energy storage solutions to meet the challenges of modern energy supply systems with high amounts of renewable energy. These energy storage systems need to address variable power, capacity and profitability requests. Zinc-air batteries with a specific energy density higher than lithium-ion and low cost, highly available, eco-friendly active materials are suitable to fulfill these requirements. The use of a flow battery type with zinc-particles suspended in alkaline solution (zinc-slurry) in addition with oxygen reduction electrodes developed for the chloralkali process allows the development of high-power zinc-air batteries. This setup also enables the independent scaling of capacity and power. The cooperative research project ZnMobil, supported by the Federal Ministry of Economic Affairs and Energy in Germany, combines the experience of industrial and academic partners (Covestro Deutschland AG; Grillo-Werke AG; VARTA Microbattery GmbH; Accurec Recycling GmbH; Technical University Freiberg, Gottfried Wilhelm Leibniz University Hannover; University of Duisburg-Essen; The fuel cell research center ZBT GmbH) to develop a low-cost zinc-air flow battery with high performance. Here we present the electrochemical performance of the new zinc-air flow battery with respect to different zinc-slurry compositions. The battery system consists of a 100 cm² copper plate as current collector for the zinc-suspension electrode and an oxygen reduction electrode with gas-diffusion layer (supplied by Covestro). The zinc-slurry contains zinc particles (supplied by Grillo) suspended in alkaline solution (30 wt-% KOH) and stabilized with polyacrylic acid. Current voltage curves and depth of discharge were measured as a function of slurry composition (e.g. zinc content, additives) and different flow velocities of the zinc slurry. Corresponding zinc-slurry conductivities were evaluated in a flow-through conductivity measurement setup. Depending on the selected parameters, it is possible to achieve discharge current densities higher than 4 kA/m².

In the recent years, rechargeable lithium-ion batteries (LIBs) have gained in importance for electronic devices and electric vehicles. Thus, research and development focuses on improving energy and power densities as well as durability of LIBs. Especially for high energy and power densities, the electrode materials must possess a high specific storage capacity and a high coulombic efficiency. However, state-of-the-art anode and cathode electrode materials, e.g. graphite and LiFePO4 exhibit a high coulombic efficiency but a rather low theoretical storage capacity (372 and 170 mAh⋅g-1, respectively). In the last decade silicon has become a promising anode material due to its high theoretical specific capacity of 3579 mAh⋅g-1at ambient temperature. However, this high specific storage capacity owing to host up to 3.75 lithium atoms per silicon atom leads to extreme volume expansion up to 300 % during lithiation, which results in pulverization and delamination of the electrode material after few cycles. Various approaches have been conducted to overcome these issues e.g. by using nano-sized active material or carbon coated silicon composite material. In addition to the materials science the electrode structure is of particular importance for the electrochemical performance. Electrode composition, binding mechanism due to the use of suitable binder polymers, particle size distribution of the active material or the modification of the SEI are some exemplary parameters to stabilize the electrode structure and to handle such high mechanical stress during lithiation/delithiation. Finally, the developed silicon anode must be implemented into a full cell by combining the anode with a suitable cathode. Because in a commercial LIB only the cell voltage is controllable, the electrode balancing of the full cell, that means the capacity ratio of the negative to positive electrode (N/P ratio) and the electrochemical voltage window in which the full cell is operated, is practically important to achieve a long cycle life and a high coulombic efficiency for the battery. For example, it can be ensured by adjusting the electrochemical potential window and choosing a well-balanced electrode design (normally N/P>1) that irreversible capacity losses can be prevented, which are correlated to lithium plating on the anodes surface during the charging process. Here we present electrochemical investigations of high capacity and high efficiency graphene coated silicon nanocomposite based electrodes prepared by using a water based wet chemical doctor blade manufacturing process. The commercially available Si/C-composite is mixed with graphite to obtain a Si/C-anode that provides a capacity of 1000 mAh⋅g-1 with an average coulombic efficiency >99 % over more than 500 cycles in half cells. The developed Si/C-anode is combined with a LiFePO4-cathode to build high-energy full cells. Investigations focus on the influence of the N/P ratio and the voltage window on the electrochemical performance of Si/C-LiFePO4 full cells. It will be shown that the developed Si/C-anode improves the energy density of the full cell regarding to a comparable C6-LiFePO4 full cell over more than 200 cycles.

The oxidation of ferrocene and diphenylanthracene (DPA) has been studied in aprotic solvents using impedance spectroscopy. Only dichloromethane proved to be suited to reproducible measurements. The impedance data were analyzed graphically and numerically according to the Randles model of a single electron transfer. The rate constants obtained for the oxidation of ferrocene and DPA in dichloromethane were 0.67 cm s −1 and 1.8 cm s −1 respectively. The magnitude of the rate constant of ferrocene is in good agreement with reported values from cyclic voltammetry at ultramicroelectrodes.

High temperature polymer electrolyte membrane fuel cells (HT PEMFCs) offer tremendous flexibility when used as energy converters in stationary as well as mobile power devices. Coupling HT PEMFC stacks with fuel processors that use liquid as well as gaseous fuels to generate hydrogen rich gas is a promising prospect, which paves the way for a possible hydrogen economy. The current paper deals with the performance aspects of a 150 Wel HT PEMFC stack, which potentially could be coupled to (i) a natural gas reformer, (ii) a propane reformer, or (iii) a methanol reformer. A 12 cell HT PEMFC stack with a total active area of about 600 cm2 was operated in a test rack, and the results show that HT PEMFCs are principally suited for operation with reformates.