Electrolytes and electrochemical Methods

We develop liquid and solid polymer electrolytes for lithium-ion and post-Li battery technologies. In our group electrolytes are tested for their stability and degradation mechanisms in energy storage systems with the aim to improve the battery cycle life and battery safety.

Fig. 1. a) Degradation in Graphite-Potassium half cells in dependence of the electrode composition (top). b) 1H-NMR spectra of aged, carbonate-based solvent components in contact with potassium metal (bottom).
Fig. 2. Picture of a polymer electrolyte film after casting and drying (top). Change of characteristic electrolyte properties with composition (bottom).

Electrolytes are one of the three primary components in Li- and post-Li batteries. They are responsible for the ionic transport between the two electrode materials, namely anode and cathode that store cations in their host structure. The mechanical and (electro)chemical properties of the electrolyte are paramount for long cycle life and battery safety. The transport properties of ions in a given electrolyte material determine its ionic conductivity and thus the so-called rate-capability of the battery, including its fast charging capabilities.

The aim of our research is to tailor the electrolyte properties for improved safety, to boost durability in the highly demanding environment of high-voltage batteries and to tweak the fast charging capabilities. This requires fundamental understanding of the chemical and physical processes in the material during battery operation and under different operation conditions, for which a broad spectrum of chemical and electrochemical analytical methods is employed.


Electrolytes for Lithium and Post-Li Batteries

Battery aging is a result of decomposition reactions of electrolyte components at the interfaces of anode and cathode, when their electrochemical stability window is exceeded. As a result, charge carriers (like lithium ions) that have contributed previously to the capacity of the battery are permanently lost as they deposit as salts on the electrode surface and thus participate no longer the cell reactions.

This is a particular challenge for so-called post-Li technologies, such as the sodium- or potassium-ion battery, that are supposed to complement current Li-ion technology in fields where scalability and low cost are essential. Unfortunately, decomposition reactions in these systems are more pronounced and for this reason the cycle life of post-Li batteries has so far not reached the same level as for established Li-ion batteries.

Understanding decomposition mechanisms of electrolyte components is therefore a major objective in our research in order to select suitable materials and additives for next-generation electrolyte mixtures. For this we combine electrochemical characterization techniques (Fig. 1a), with analysis of liquid and solid decomposition products that accumulate either in the electrolyte or on the electrode surface, using nuclear magnetic resonance (NMR) spectroscopy (Fig. 1b), photoelectron spectroscopy (XPS) or electrochemical impedance spectroscopy (EIS). In addition, we apply gas chromatography mass spectrometry (GC-MS) and calorimetric techniques in collaboration with other research groups in the Post-Li Storage Cluster of Excellence (POLiS).

Electrolyte Development: From Liquid to Solid Polymer Electrolytes

Moving from conventional liquid electrolyte mixtures to solid electrolytes is considered an important technological transition from state-of-the-art Li-ion batteries towards next-generation energy storage systems with improved safety properties, yet potentially higher energy densities and longer cycle life.

One class of solid electrolytes are polymer electrolytes that dissolve, similar to their liquid counterparts, electrolyte salts in a solid host matrix. Under an applied voltage, i.e. during battery operation, charge carriers can travel through the solid matrix. Polymers exhibit several benign properties compared to liquid electrolytes, including their inherently higher safety (no components with high vapor pressure or low flashpoint; lower toxicity), ease of processability and a broader electrochemical stability window that is generally associated with lower degrees of side reactions and thus better capacity retention. A prominent example of the successful integration of polymer electrolytes into Li-Ion batteries is the Belloré Bluecar.

Our research activities currently focus on polymer electrolytes for potassium-ion batteries. The aim is to improve the ionic conductivity of the materials to a degree that allows room temperature applications, while maintaining good mechanical integrity in a broad temperature range, as well as electrochemical stability in a broad voltage range. The material development is supported by a portfolio of different methods from the field of polymer chemistry and electrochemistry, such as the characterization of rheological, thermal and morphological properties (e.g. using differential scanning calorimetry (DSC)), infrared spectroscopy to investigate polymer-salt interactions, as well as electrochemical characterization techniques, including electrochemical impedance spectroscopy (ionic conductivity) and voltammetric techniques to test for electrochemical stability. The polymer electrolytes are further tested directly in battery configurations for their suitability in actual battery applications.


All-solid potassium batteries – a polymer electrolyte approach (POLiS – Post Lithium Storage Cluster of Excellence)

Potassium-Ion Batteries: Sustainable Strategies (KIBSS; DFG Project #448719339)

Lithium recovery and battery-grade materials production from European resources (LiCORNE)

Chemical Prelithiated 3D Lithiophilic/-Phobic Interlayer Enables Long-Term Li Plating/Stripping
Schöner, S.; Schmidt, D.; Chen, X.; Dzieciol, K.; Schierholz, R.; Cao, P.; Ghamlouche, A.; Jeschull, F.; Windmüller, A.; Tsai, C.-L.; Liao, X.; Kungl, H.; Zhong, G.-M.; Chen, Y.; Tempel, H.; Yu, S.; Eichel, R.-A.
2024. ACS Nano, 18 (27), 17924–17938. doi:10.1021/acsnano.4c04507
Degradation of Styrene-Poly(ethylene oxide)-Based Block Copolymer Electrolytes at the Na and K Negative Electrode Studied by Microcalorimetry and Impedance Spectroscopy
Xing, S.; Khudyshkina, A.; Rauska, U.-C.; Butzelaar, A. J.; Voll, D.; Theato, P.; Tübke, J.; Jeschull, F.
2024. Journal of The Electrochemical Society, 171 (4), Art.-Nr.: 040516. doi:10.1149/1945-7111/ad3b72
Multiscale Investigation of Sodium‐Ion Battery Anodes: Analytical Techniques and Applications
Schäfer, D.; Hankins, K.; Allion, M.; Krewer, U.; Karcher, F.; Derr, L.; Schuster, R.; Maibach, J.; Mück, S.; Kramer, D.; Mönig, R.; Jeschull, F.; Daboss, S.; Philipp, T.; Neusser, G.; Romer, J.; Palanisamy, K.; Kranz, C.; Buchner, F.; Behm, R. J.; Ahmadian, A.; Kübel, C.; Mohammad, I.; Samoson, A.; Witter, R.; Smarsly, B.; Rohnke, M.
2024. Advanced Energy Materials, Art.-Nr.: 2302830. doi:10.1002/aenm.202302830
Multivalent Cation Transport in Polymer Electrolytes – Reflections on an Old Problem
Jeschull, F.; Hub, C.; Kolesnikov, T. I.; Sundermann, D.; Hernández, G.; Voll, D.; Mindemark, J.; Théato, P.
2023. Advanced Energy Materials. doi:10.1002/aenm.202302745
Unraveling Propylene Oxide Formation in Alkali Metal Batteries
Stottmeister, D.; Wildersinn, L.; Maibach, J.; Hofmann, A.; Jeschull, F.; Groß, A.
2023. ChemSusChem, 17 (3), Art.Nr.: e202300995. doi:10.1002/cssc.202300995
Impact of Nano‐sized Inorganic Fillers on PEO‐based Electrolytes for Potassium Batteries
Khudyshkina, A. D.; Rauska, U.-C.; Butzelaar, A. J.; Hoffmann, M.; Wilhelm, M.; Theato, P.; Jeschull, F.
2024. Batteries and Supercaps, 7 (1), Art.-Nr.: e202300404. doi:10.1002/batt.202300404
Electrochemical investigation of fluorine-containing Li-salts as slurry cathode additives for tunable rheology in super high solid content NMP slurries
Colombo, F.; Müller, M.; Weber, A.; Keim, N.; Jeschull, F.; Bauer, W.; Ehrenberg, H.
2023. Energy Advances, 2, 2093–2108. doi:10.1039/d3ya00246b
Revealing the Formation of Dialkyl Dioxahexane Dioate Products from Ethylene Carbonate Based Electrolytes on Lithium and Potassium Surfaces
Hofmann, A.; Müller, F.; Schöner, S.; Jeschull, F.
2023. Batteries & Supercaps, 6 (12), Art.Nr.: e202300325. doi:10.1002/batt.202300325
From lithium to potassium: Comparison of cations in poly(ethylene oxide)-based block copolymer electrolytes for solid-state alkali metal batteries
Khudyshkina, A. D.; Butzelaar, A. J.; Guo, Y.; Hoffmann, M.; Bergfeldt, T.; Schaller, M.; Indris, S.; Wilhelm, M.; Théato, P.; Jeschull, F.
2023. Electrochimica Acta, 454, Article no: 142421. doi:10.1016/j.electacta.2023.142421
Interphase formation with carboxylic acids as slurry additives for Si electrodes in Li-ion batteries. Part 2: a photoelectron spectroscopy study
Jeschull, F.; Pham, H. Q.; Ghamlouche, A.; Thakur, P. K.; Trabesinger, S.; Maibach, J.
2023. Journal of Physics: Energy, 5 (2), 025002. doi:10.1088/2515-7655/acbbee
Interphase formation with carboxylic acids as slurry additives for Si electrodes in Li-ion batteries. Part 1: performance and gas evolution
Jeschull, F.; Zhang, L.; Kondracki, Ł.; Scott, F.; Trabesinger, S.
2023. Journal of Physics: Energy, 5 (2), Art.-Nr.: 025003. doi:10.1088/2515-7655/acbbed
Degradation Phenomena in Silicon/Graphite Electrodes with Varying Silicon Content
Ghamlouche, A.; Müller, M.; Jeschull, F.; Maibach, J.
2022. Journal of The Electrochemical Society, 169 (2), Art.-Nr.: 020541. doi:10.1149/1945-7111/ac4cd3
Potential and Limitations of Research Battery Cell Types for Electrochemical Data Acquisition
Smith, A.; Stueble, P.; Leuthner, L.; Hofmann, A.; Jeschull, F.; Mereacre, L.
2023. Batteries & Supercaps, 6 (6), e202300080. doi:10.1002/batt.202300080
Performance-Determining Factors for Si–Graphite Electrode Evaluation: The Role of Mass Loading and Amount of Electrolyte Additive
Surace, Y.; Jeschull, F.; Novák, P.; Trabesinger, S.
2023. Journal of The Electrochemical Society, 170 (2), Art.-Nr.: 020510. doi:10.1149/1945-7111/acb854
Glyoxylic acetals as electrolytes for Si/Graphite anodes in lithium-ion batteries
Gehrlein, L.; Leibing, C.; Pfeifer, K.; Jeschull, F.; Balducci, A.; Maibach, J.
2022. Electrochimica Acta, 424, Art.-Nr.: 140642. doi:10.1016/j.electacta.2022.140642
Poly(ethylene oxide)-Based Electrolytes for Solid-State Potassium Metal Batteries with a Prussian Blue Positive Electrode
Khudyshkina, A. D.; Morozova, P. A.; Butzelaar, A. J.; Hoffmann, M.; Wilhelm, M.; Theato, P.; Fedotov, S. S.; Jeschull, F.
2022. ACS Applied Polymer Materials, 4 (4), 2734–2746. doi:10.1021/acsapm.2c00014
Comparing the Solid Electrolyte Interphases on Graphite Electrodes in K and Li Half Cells
Allgayer, F.; Maibach, J.; Jeschull, F.
2022. ACS applied energy materials, 5 (1), 1136–1148. doi:10.1021/acsaem.1c03491
Styrene-Based Poly(ethylene oxide) Side-Chain Block Copolymers as Solid Polymer Electrolytes for High-Voltage Lithium-Metal Batteries
Butzelaar, A. J.; Röring, P.; Mach, T. P.; Hoffmann, M.; Jeschull, F.; Wilhelm, M.; Winter, M.; Brunklaus, G.; Théato, P.
2021. ACS applied materials & interfaces, 13 (33), 39257–39270. doi:10.1021/acsami.1c08841
IMLB conference 2022

Electrolyte Degradation and Interphase Formation Processes in Potassium-Ion Batteries