Browsing by Author "Gerle, Martina"

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Open Access
Identification of the underlying processes in impedance response of sulfur/carbon composite cathodes at different SOC
(2022) Gerle, Martina; Wagner, Norbert; Häcker, Joachim; Nojabaee, Maryam; Friedrich, K. Andreas
For lithium-sulfur batteries, porous carbon/sulfur composite cathodes are the primary solution to compensate the non-conductive nature of sulfur. The composition and structure of this class of cathodes are crucial to the electrochemical performance, achieved energy density and the stability of the cell. Electrochemical impedance spectroscopy is employed to investigate and correlate the electrochemical performance of lithium-sulfur batteries to the composition and microstructure of differently fabricated carbon/sulfur composite cathodes. A transmission line model is applied to identify different underlying electrochemical processes appearing in the impedance response of a range of porous carbon/sulfur cathodes. The integration of a lithium ring serving as a counter electrode coupled with advanced wiring has allowed an artifact-free recording of the cathode impedance at different states of charge with the aim to investigate the evolution of impedance during discharge/charge and the kinetics of charge transfer depending on the infiltration method and the utilized carbon host. It is shown that impedance response of this class of cathodes is highly diverse and the plausible underlying processes are discussed in details. To this end, quasi-solid-state and various polysulfide-based charge transfer mechanisms are identified and their time constants are reported.
Open Access
Impact of the sulfurized polyacrylonitrile cathode microstructure on the electrochemical performance of lithium-sulfur batteries
(2025) Moschner, Robin; Gerle, Martina; Danner, Timo; Simanjuntak, Esther Kezia; Michalowski, Peter; Latz, Arnulf; Nojabaee, Maryam; Kwade, Arno; Friedrich, K. Andreas
The growing demand for advanced energy storage systems requires the development of next‐generation battery technologies with superior energy density and cycle stability, with lithium-sulfur (Li-S) batteries representing a promising solution. Sulfur‐containing polyacrylonitrile cathodes (SPAN) for Li-S batteries are a significant advancement for this next‐generation battery chemistry, addressing the major issue of limited cycle life encountered in conventional carbon/sulfur composite cathodes. In the presented study, the influence of available ionic and electronic conduction pathways within the cathode on the electrochemical performance of SPAN‐based Li-S batteries is studied in details. To this end, a series of SPAN cathodes with different microstructures is prepared by adapting the compression degree of calendering. Mechanical and morphological characterizations confirm a pronounced springback effect due to a characteristic elastic deformation behavior of SPAN. Electrochemical impedance spectroscopy (EIS) shows increased cathode impedance values with multiple overlapping processes in the high‐ to mid‐frequency region in highly compressed SPAN cathodes. Moreover, while the (first) discharge capacity is unaffected, the subsequent charge capacity decreases substantially for highly compressed cathodes. The electrochemical experiments and electrochemical continuum simulations confirm that this phenomenon is mainly due to the disturbance of the electronic percolation pathways caused by the springback behavior during calendering.
Open Access
Intensification of alkaline electrolyzer with improved two‑phase flow
(2025) Egert, Franz; Ullmer, Dirk; Marx, Sven; Taghizadeh, Ehsan; Morawietz, Tobias; Gerle, Martina; Le, Thi Anh; Campo Schneider, Lucia Paula; Biswas, Indro Shubir; Wirz, Richard E.; Spieth, Philipp; Marquard‐Möllenstedt, Tonja; Brinner, Andreas; Faccio, Ricardo; Fernández‐Werner, Luciana; Esteves, Martín; Razmjooei, Fatemeh; Ansar, Syed Asif
Green hydrogen produced through water electrolysis offers a promising pathway to global decarbonization. Among various electrolyzers, alkaline water electrolysis (AWE) is the most established and commercially mature. To reduce the cost of hydrogen production from AWE, it is crucial to increase operational current density while maintaining or lowering voltage to increase hydrogen yield and reduce energy consumption. Such efforts are focused on reducing the ohmic resistance at high current densities through the implementation of alkaline membranes. However, this work underlines that the ohmic resistance at high current densities is also influenced by the losses associated with the evolution of bubbles at the electrode surface and two‐phase mass transfer. This is shown by investigating the impact of tortuosity and bubble point of porous electrodes on AWE performance. Low‐tortuosity porous nickel electrodes are fabricated and analyzed for their ability to reduce capillary pressure and bubble point, resulting in lower energy losses and improved efficiency. The cell reaches an industrially appealing relevant current density of 2 A cm -2 at ≈2 V. Besides test in single cells, the advantageous effect of these low tortuosity porous nickel electrodes are also validated in a kW‐class AWE stack, confirming their effectiveness in enhancing overall system performance.