• Energy Research

A series of vanadium redox‐flow battery (VRFB) electrolytes at 1.55 m vanadium and 4.5 m total sulfate concentration are prepared from vanadyl sulfate solution and tested under conditions of appearance of “power drop” effect (discharge at high current density from high state‐of‐charge). A correlation between the initial electrolyte composition, the thermal stability of catholyte, and the susceptibility of VRFB to exhibit a “power drop” effect is derived. The increase in total acidity to 3 m, expressed as concentration of sulfuric acid in precursor vanadyl sulfate solution, enables “power drop”‐free operation of VRFB at least at 75 mA cm−2. Thermally‐induced degradation of electrolyte is evaluated based on decrease in vanadium concentration in the electrolyte series after exposure to the temperature of 45 °C and based on characterization of catholytes series using 51V, 17O, and 1H nuclear magnetic resonance spectroscopy.

Abstract The feasibility of an alkaline S 2 O 4 2− /air-fuel cell was evaluated at room temperature, using a cell with an anion exchange membrane and a platinum oxygen reduction reaction catalyst. The tests performed were open circuit voltage analysis, linear sweep voltammetry, discharge analysis and electrochemical impedance spectroscopy (EIS) with registration of anode half-cell potential. With 0.85 M Na 2 S 2 O 4 in 2 M KOH, the cell achieved a maximum power density of 2 mW cm −2 , and the open circuit cell voltage was about 0.9 V. In a potentiostatic discharging at 0.2 V cell voltage, an energy efficiency of 12.3% was achieved at an energy density of 8.6 Wh L −1 . The low power density was mainly due to the low reaction kinetics of dithionite oxidation at graphite electrodes. The low energy efficiency was mainly caused by a low cathode potential, which probably resulted from mixed potential formation and the low anode kinetics.

The detailed mechanistic understanding of the electrochemical reactions occurring in lithium-ion battery electrodes is fundamental for their further improvement. Conversion/alloying materials (CAMs), such as Zn0.9Fe0.1O, one of the most recent alternatives for classic graphite anodes, offer superior specific capacity and rate capability. However, despite fast kinetics, CAMs suffer from a large voltage hysteresis upon de-/lithiation and improvable Coulombic efficiencies when cycled in a large voltage window. Here, we use isothermal microcalorimetry together with operando X-ray diffraction as well as ex situ 7Li NMR and 57Fe Mössbauer spectroscopies to investigate the asymmetric reaction mechanism of the lithiation and delithiation of Zn0.9Fe0.1O during electrochemical cycling. We demonstrate that the measured heat flow is correlated with compositional changes of the electrode material. This combination of highly complementary techniques allows us to propose a new nucleation site model for the initial lithiation of Zn0.9Fe0.1O. Modeling the heat flow provides concrete evidence for the deleterious impact of high anodic cutoff potentials (>2 V), resulting in a continuous quasireversible solid electrolyte interphase formation. The presented methodology is suggested to provide improved insights into the reaction mechanism of conversion- and alloying-type energy-storage materials.

The flow field design and material composition of the electrode plays an important role in the performance of redox flow batteries, especially when using highly viscous liquids. To enhance the discharge power density of zinc slurry air flow batteries, an optimum slurry distribution in the cell is key. Hence, several types of flow fields (serpentine, parallel, plastic flow frames) were tested in this study to improve the discharge power density of the battery. The serpentine flow field delivered a power density of 55 mW∙cm−2, while parallel and flow frame resulted in 30 mW∙cm−2 and 10 mW∙cm−2, respectively. Moreover, when the anode bipolar plate material was changed from graphite to copper, the power density of the flow frame increased to 65 mW∙cm−2, and further improvement was attained when the bipolar plate material was further changed to copper–nickel. These results show the potential to increase the power density of slurry-based flow batteries by flow field optimization and design of bipolar plate materials.

This research paper investigates the influence of varying silicon oxide (SiOx) content on the performance and aging of lithium-ion cells. In-depth investigations encompass charge and discharge curves, thickness changes, electrolyte degradation, gas evolution, and chemical analysis of cells with different silicon oxide proportions in the anode and their associated cathodes. The results show that a higher silicon oxide content in the anode increases the voltage hysteresis between charge and discharge. Moreover, the first-cycle efficiencies decrease with a higher silicon oxide content, attributed to irreversible LixSiy formation and the subsequent loss of active lithium from the cathode during formation. The anodes experience higher thickness changes with increased silicon oxide content, and peaks in differential voltage curves can be correlated with specific anode active materials and their thickness change. A gas analysis reveals conductive salt and electrolyte intermediates as well as silicon-containing gaseous fragments, indicating continuous electrolyte decomposition and silicon oxide aging, respectively. Additionally, a chemical analysis confirms increased silicon-derived products and electrolyte degradation on electrode surfaces. These findings underscore the importance of a holistic aging investigation and help understand the complex chemical changes in electrode materials for designing efficient and durable lithium-ion cells.

Polybromides formation in aqueous bromine electrolytes and influence on H2/Br2redox flow battery performance is investigated the first time.

AbstractDue to the rapidly increasing demand for electric vehicles, the need for battery cells is also increasing considerably. However, the production of battery cells requires enormous amounts of energy, which is expensive and produces greenhouse gas emissions. Here, by combining data from literature and from own research, we analyse how much energy lithium-ion battery (LIB) and post lithium-ion battery (PLIB) cell production requires on cell and macro-economic levels, currently and in the future (until 2040). On the cell level, we find that PLIB cells require less energy than LIB cells per produced cell energy. On the macro-economic level, we find that the energy consumption for the global production of LIB and PLIB cells will be 130,000 GWh if no measures are taken. Yet, it is possible to optimize future production and save up to 66% of this energy demand.

Along with the increased usage of lithium‐ion batteries and their development in energy densities, safety issues arise that have to be investigated. The most serious battery safety event is called thermal runaway. Herein, a chemical thermal runaway model with ten decomposition reactions is developed. It is coupled with thermal simulations in order to predict temperature curves as well as amount and composition of released gases during thermal runaway. Simulations are validated by thermal abuse experiments in an autoclave. Detailed temperature measurements and gas analysis are included. Simulations and experimental results prove to be in good agreement. The model is further applied to investigate thermal runaway behavior of cells with different energy densities.