The INNENERMAT project, funded by the German Federal Ministry of Education and Research under the grant number 03XP0298A, ran from 1 October 2020 to 31 August 2023. Its main objective was to advance lithium‑sulfur (Li‑S) battery technology by developing flexible cathodes, flexible anodes, and solid‑polymer electrolytes (SPEs) that could be integrated into pouch cells. The German Aerospace Center (DLR) led the technical work, collaborating with partners such as ASTREA, CSIC‑INCAR, BINDER ITZ, and CELANESE. The project aimed to raise the technology readiness level (TRL) from 3 to 6–7 and to achieve a storage capacity of 1 000 Ah kg⁻¹ of sulfur and 1 000 charge‑discharge cycles in laboratory cells.

The technical effort was organized into six work packages. Work package 1 focused on materials synthesis and component optimisation, producing porous carbon matrices and sulfur‑infiltrated composites. Work package 2 developed intelligent textile electrodes and integrated architectures, while work package 3 handled the manufacture of solid‑state and Li‑S cells, testing, and safety assessments. Work package 4 demonstrated proof‑of‑concept Li‑S and solid‑state systems and performed preliminary techno‑economic analyses. Work package 5 managed dissemination and exploitation, and work package 6 coordinated project administration. DLR carried out material‑science and process‑engineering studies to evaluate the performance and compatibility of the new porous carbons, flexible anodes, gel and polymer electrolytes in Li‑S cells. Experimental work produced flexible cathodes using conductive carbon particle and weave structures, employing gas‑infiltration and polysulfide impregnation techniques. A flexible anode concept was also developed and electrochemically characterised. The solid‑polymer electrolyte, based on a lithiated Nafion membrane (SLIC‑SPE), was characterised to reduce polysulfide mobility and mitigate the shuttle effect. The combination of gas‑phase infiltrated sulfur‑carbon composite cathodes with the SPE allowed the use of carbonate‑based solvents in a quasi‑FeS concept, improving environmental friendliness and scalability.

Electrochemical testing of the integrated pouch cells demonstrated the targeted performance: a specific capacity of 1 000 Ah kg⁻¹ of sulfur and a cycle life of 1 000 cycles under laboratory conditions. These results confirmed the feasibility of the flexible cell architecture and validated the design concepts. The project also produced a demonstrator cell that was delivered to partner ASTREA for further development and potential industrialisation.

Collaboration was central to the project’s success. DLR coordinated all six work packages and organised monthly meetings, which were largely held online during the COVID‑19 pandemic, saving travel costs. The project budget was 437 181,10 €, of which 429 179,49 € were spent. Adjustments were made to account for increased material needs for sulfur‑carbon composites, additional glassware, and replacement of worn components during thermogravimetric analysis. Six thousand euros of travel costs were reallocated to material expenses with the approval of the project sponsor in Jülich. The partners plan to continue joint research, submitting a new M‑ERA.NET proposal (ProPoLiS) that builds on the carbon/sulfur composite work. Early discussions with industrial partners BINDER ITZ and CELANESE indicate potential for future collaboration and technology transfer. The project’s outcomes provide a solid foundation for further development of high‑energy, flexible Li‑S batteries and demonstrate a clear pathway toward commercial application.