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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.

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.

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.

Methanol is a liquid fuel which could also be produced from renewable energy sources and has appreciably high energy density. It has a high H : C ratio of 4 : 1 without any C-C bond. It is easier to reform when compared to CH4 to produce H2 rich gas that could be fed into a high temperature polymer electrolyte membrane fuel cell or HT-PEMFC. A typical IRMFC module consists of a HT-PEMFC thermally integrated with a methanol evaporator and reformer in a closed thermal loop. Simulations show that the total heat demand of the evaporator and the methanol steam reformer would require only 20% of the heat generated by the HT-PEMFC where the geometrical area of the HT-PEMFC is almost equal to that of the geometrical area of the reforming catalyst. In the current work a novel IRMFC which is operated in the 210-220°C range is presented. Operating an IRMFC at these high temperatures would mean novel materials and components to be employed within the HT-PEMFC as well as within the methanol reformer unit. The high temperature stable membrane electrode assemblies were developed by Advent technologies in Greece. The high temperature stable bipolar plates were developed by ZBT in Germany within the scope of a current EU funded project. When operated at 220°C on 350 mA/cm² of load current, the novel HT-PEMFC could deliver 210 mW/cm² at 0.6 V. As for the methanol reforming unit operated at 220°C, when fed with methanol-water mixture with a steam to carbon ratio of 1.5, the methanol conversion rate was around 90%. The performance analyses of the IRMFC single unit as well as that of the 5 cell unit demonstrate the potential to developing a compact light weight power generating unit offering double the gravimetric and volumetric energy densities offered by the current direct methanol fuel cell based units.

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