Development and Fundamental Understanding of Self-healing Flexible Li-S Batteries with High Cycle Stability (FlexBatt)

• Applicant: Professor Dr. Michael Sommer, since 9/2021
• Subject Area: Preparatory and Physical Chemistry of Polymers ; Synthesis and Properties of Functional Materials ; Polymer Materials
• Term: from 2019 to 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 423426992

The design of successful future Li-S batteries with high energy density has the prospect to significantly improve existing battery technology and boost environmentally friendly automotive development. Li-S batteries could triple the energy density relative to existing Li-ion batteries combined with high reversibility of fast charging-discharging cycles and lifetime of thousands of cycles. Recent progress on Li-S batteries indicates a complex mechanism of operation, and hence calls for further in-depth mechanistic studies and material development of all battery components alike. Major performance- and stability-limiting factors are related to conductivity, polysulfide dissolution and redox shuttle phenomena, volume expansion and electrode passivation by (poly)sulfides. Flexible batteries allow to adopt any desired shape. The use of self-healing materials that undergo autonomous self-repairing to heal cracks created by volume expansion could retain conductive pathways for a high number of cycles. The herein proposed concept "FlexBatt" encompasses the development of flexible components for an entire Li-S battery. Anode, cathode, separator and solid polymer electroyte will be designed in a way that flexibility is realized by virtue of self-healing materials. Moreover, the correlation between flex behavior and cell performance will be studied by rheology (rheo-impedance) and in-operando electrochemical and spectroscopic approaches. A flexible, free-standing, low binder content cathode will be developed based on flexible sulfur-copolymer-CNT networks. These will be combined with novel elastomeric solid electrolytes and a lithium-deposited textile based anode. A custom-build setup combining rheology and potentiostat will be used to understand the self-healing behavior of the electrodes by creep and relaxation phenomena. Impedance data before appying deformation, after deformation and after self-healing will be monitored by impedance analyses. During electrochemical cycling, ion transport across the membrane and morphological changes will be investigated by in-operando techniques to understand the correation between cycle performance and flex behavior. Intermittent analyses of the electrodes to ensure the self-healing properties will be conducted by small anagle X-ray scattering, microscopy and spectroscopic approaches. The post-mortem analysis of the cell parts after multiple charging-discharging cycles and at different depth of discharge will be carrried out to understand the functionality and durability of the cell operated at different bending angles. The complete study aims at understanding the importance of mechano-chemical stability of the entire flexible battery and finally will provide insight into the mechanism and fate of irreversible reactions of sulfur/organosulfur species limiting battery performance and life time.

• DFG Programme: Research Grants
• Ehemaliger Antragsteller: Privatdozent Soumyadip Choudhury, Ph.D., until 8/2021